DR. LARDNER'S HANDBOOK OF NATURAL PHILOSOPHY AND ASTRONOMY.*

Ir was justly observed by Professor Playfair, in his Dissertation on the Progress of Mathematical and Physical Science, which prefaces the Supplement to the "Encyclopædia Britannica," that, in order to render such subjects interesting, they need only be treated with clearness and precision. This is precisely Dr. Lardner's forte, and the secret of his popularity as a writer on science.

The present work, which embraces only a portion of his subject, viz., Mechanics, Hydrostatics, Hydraulics, Pneumatics, Sound, and Optics, illustrated by four hundred engravings, and written in at once the most lucid and simple language, yet at the same time with every regard to scientific detail and exposition, cannot fail to be the Handbook of the day. At the same time-the author having had in view the satisfaction of those who desire to obtain a knowledge of the elements of physics without pursuing them through their mathematical consequences-the work is equally adapted for general perusal. "The work," says Dr. Lardner, "has been also composed with the object of supplying that information relating to physical and mechanical science which is required by the medical and law student, the engineer, and artisan; by those who are preparing for the universities, and, in short, by those who, having already entered upon the active pursuits of business, are still desirous to sustain and improve their knowledge of the general truths of physics, and of those laws by which the order and stability of the natural world are maintained."

As an example of clear and lucid writing when applied to science, we may quote a passage on the distinctness of vision compared with the magnitude of the pictures on the retina:

Nothing (says Dr. Lardner) can be more calculated to excite our wonder and admiration than the distinctness of our perception of visible objects, compared with the magnitude of the picture on the retina, from which immediately we receive such perception.

If we look at the full moon on a clear night, we perceive with considerable distinctness by the naked eye the lineaments of light and shade which characterises its disc.

Now let us consider only for a moment what are the dimensions of the picture of the moon formed on the retina, from which alone we derive this distinct perception.

Example of the Picture of the Full Moon on the Retina.-The disc of the moon subtends a visual angle of half a degree, and consequently, according to what has been explained, the diameter of its picture on the retina will be 1-230th part of an inch, and the entire superficial magnitude of the image from which we derive this distinct perception is only the 1-52,900th part of a square inch; yet within this minute space, we are able to distinguish a multiplicity of still more minute details. We perceive, for example, forms of light and shade, whose linear dimensions do not exceed one-tenth part of the apparent diameter of the moon, and which therefore occupy upon the retina a space whose diameter does not exceed the 1-5,000,000th part of a square inch.

Example of the Human Figure.-To take another example, the figure of a man seventy inches high, seen at a distance of forty feet, produces an image upon the retina the height of which is about one-fourteenth part of an inch. The face of such an image is included in a circle whose diameter is about one-twelfth of the height, and therefore occupies on the retina a circle whose diameter is about the 1-170th part of an inch; nevertheless, within this circle, the eyes, nose, and lineaments are distinctly seen. The diameter of the eye is about one-twelfth of

*Handbook of Natural Philosophy and Astronomy. By Dionysius Lardner, D.C.L., &c. Taylor, Walton, and Maberly.

that of the face, and therefore, though distinctly seen, does not occupy upon the retina a space exceeding the 1-4,000,000th of a square inch.

If the retina be the canvas on which this exquisite miniature is delineated, how infinitely delicate must be its structure, to receive and transmit details so minute with such marvellous precision; and if, according to the opinion of some, the perception of these details be obtained by the retina feeling the image formed upon the choroid, how exquisitely sensitive must be its touch!

Again in a more general field of inquiry, and exemplifying the interest of microscopic research:

Microscopic research has diclosed the existence of animals, a million of which do not exceed the bulk of a grain of sand, and yet each of these is composed of members as admirably suited to their mode of life as those of the largest species. Their motions display all the phenomena of vitality, sense, and instinct. In the liquids which they inhabit they are observed to move with the most surprising speed and agility; nor are their motions and actions blind and fortuitous, but evidently governed by choice and directed to an end. They use food and drink, by which they are nourished, and must, therefore, be supplied with a digestive apparatus. They exhibit a muscular power far exceeding in strength and flexibility, relatively speaking, the larger species. They are susceptible of the same appetites, and obnoxious to the same passions, as the superior animals, and though differing in degree, the satisfaction of these desires is attended with the same results as in our own species.

Spallanzani observes that certain animalcula devour others so voraciously that they fatten and become indolent and sluggish by over-feeding. After a meal of this kind, if they be examined with the microscope, the smaller, thus devoured, has been observed moving within the body of the greater.

The microscopic researches of Ehrenberg have disclosed most surprising examples of the minuteness of which organised matter is susceptible. He has shown that many species of infusoria exist which are so small that millions of them collected into one mass would not exceed the bulk of a grain of sand, and a thousand might swim side by side through the eye of a needle.

The shells of these creatures are found to exist fossilized in the strata of the earth in quantities so great as almost to exceed the limits of credibility.

By microscopic measurement it has been ascertained that in the slate found at Bilin, in Bohemia, which consists almost entirely of these shells, a cubic inch contains 41,000,000,000; and as a cubic inch weighs 220 grains, it follows that 180,000,000 of these shells must go to a grain, each of which would consequently weigh the 187,000,000th part of a grain.

All these phenomena lead to the conclusion that these creatures must be supplied with an organization corresponding in beauty with those of the larger species.

Here, also, are one or two examples of what may be called curiosities of

science:

Why we are not sensible of Darkness when we wink.-This continuance of the impression of external objects on the retina, after the light from the objects ceases to act, is also manifested by the fact, that the continual winking of the eyes for the purpose of lubricating the eye-ball by the eye-lid, does not intercept our vision. If we look at any external objects, they never cease for a moment to be visible to us, notwithstanding the frequent intermissions which take place in the action of light upon the retina, in consequence of its being thus intercepted by the eye-lid. Why a lighted Stick revolving produces apparently a luminous Ring.-If a lighted stick be turned round in a circle in a dark room, the appearance to the eye will be a continuous circle of light; for in this case the impression produced upon the retina by the light, when the stick is at any point of the circle, is retained until the stick returns to that point.

Flash of Lightning. In the same manner a flash of lightning appears to the eye as a continuous line of light, because the light emitted at any point of the line remains upon the retina until the cause of the light passes over the succeeding points.

These examples will suffice to show the pleasing elucidatory style adopted by the author-a style which is at the same time adopted without any sacrifice of that order and explicitness which are imperious in scientific investigation, and essential in works of a more or less educational cha

racter.

SIR ROBERT CRAVEN'S wound did not prove to be very severe, but his impatience, fretfulness, and obstinacy rendered his recovery much slower than it would otherwise have been.

During his illness, his aunt, Miss Craven, nursed him with all possible care and attention; but she wept so much, and reproached him so often with his folly and misconduct in risking his life by fighting, that she worried him and irritated his temper exceedingly. One day, about a fortnight after the duel, whilst sitting beside him as he reclined on a sofa in his dressing-room:

"Now tell me, Robert," she said, "what could have put it into your head to fight Mr. Silverdale ?"

Her nephew, as was often his custom, did not make any reply to her question, until it had been repeated twice or thrice.. At last he answered,

"What! still plaguing me with the old story? Have I not told you, fifty times, that he insulted me, and I was obliged to challenge him?"

"Be quiet, can't you?" interrupted Sir Robert, sharply. “I declare, you make such a piece of work about this duel, that you make me wish I had been killed."

"Oh, Robert! do not say so, I implore you," said Miss Craven, in a crying voice.

"Yes," replied her nephew, pleased to find that he had hit upon right mode of vexing her-"yes, I repeat it, you make me wish that I had been killed on the spot, by a bullet through my head."

"Oh, Robert, Robert! you are very unfeeling," exclaimed Miss Craven; and she wept outright.

"I tell you what," returned Craven, "if you go on in this way you'll drive me into doing something you'll be sorry for when it's too late. I'll fight another duel, and then, if I do not get killed, as I most likely shall, go off somewhere beyond seas, and never be heard of again."

66

"Oh, I will not say another word, Robert," said the weeping Miss Craven, "not a single word that you do not like, if you will be pacified." "Will you promise never again to mention this confounded duel?" "Never, never, my dear Robert-indeed I will not!"

Well, then, leave off whining and whimpering, and let us have a little peace and quiet!"

This, or a somewhat similar speech, being Sir Robert's method of signifying that he was willing to forget the dispute, and desired a reconciliation, Miss Craven's wonted composure began to return, and she said, with something like cheerfulness,

"Oh, Robert! you always were a sad, wayward boy; you must have your own way in everything. It is a great pity you were so spoiled."

"And pray who spoiled me?" returned her hopeful nephew, laughing, and then making a grimace at her.

"You are very droll, Robert," answered the old lady, delighted to see him in a good humour again; "very droll indeed. Spoiled though you may be, no person in the world can be more agreeable than you are when you are pleased."

"Pleased!" repeated Sir Robert, with a harsh laugh. "Humph! Do you think there is anything pleasant in being obliged to keep my room all day long, with nobody but a dull, cross, stupid old woman to talk to, who lectures me one-half the day and cries the other half?"

Miss Craven sat silent some minutes, and then said, in a very doleful voice, "I am sorry I am so stupid, Robert."

Sir Robert proceeded. "Then there's another thing more vexatious than all. Florence does not half love me as she ought, or as I love her. She never looks thoroughly glad to see me, and there is always a shyness and restraint in her manner towards me, that I never see her show to any one else."

"But that, my dear," replied his aunt, "is all as it should be. It is her charming modesty, and the very sign that she prefers you to others. I will say, that she is the most sensible and agreeable young lady I know, though it cannot be denied that different now from ladies are very young what they were in my young days. There was not such laughing, and chattering, and flirting, and waltzing then-oh, dear no. In those days the youth of both sexes paid some deference to their elders and superiors; now all young people think they know best about everything, and expect always to have their own way, whilst the least word of reproof, however gently and kindly given, instead of being received with humility and gratitude, is rejected with ill-humour and disdain. Oh, the vanity and conceit, the pride and wilfulness of the rising generation!"

Miss Craven sighed as she concluded, and turned up her eyes mournfully.

"I observe," said Sir Robert, who had listened to her with an air of mock gravity and attention-"I observe that you old people always undervalue the present age, and represent that antediluvian period you are pleased to term 'your young days,' as having produced characters of superlative, not to say supernatural excellence.

"Ah, Robert, you yourself are a striking example of the truth of what I say. Now I, when I was your age, should no more have thought of speaking to my aunt as you do to me than I should have thought of flying."

"Then I suppose the aunts in your young days' were not such cross, disagreeable, ugly old things as you are, were they?" asked Sir Robert, with a sneering smile.

"Is this all your respect ?" returned Miss Craven, the colour mounting in her sallow cheeks with anger and displeasure. "Is this all your respect for me?-for one who

"Take care, take care!" interrupted Sir Robert, in a loud voice, holding up his finger, as he spoke, in a warning manner. "Remember what I said I would do if I was lectured. Think of the bullet that will be sure to go through my head if I fight another duel; which I will do, as sure as fate, if you don't mind what you're about. So I give you warning, old lady."

This effectually silenced Miss Craven, and, after a short pause, Sir Robert said, in a more gentle manner,

VOL. XX.

T

"You think, then, that Florence loves me?"

"Indeed, Robert, I do."

"And yet only yesterday you advised me to delay making her a formal offer of my hand for some time longer."

"I did, and for this reason: that I should wish you first to ingratiate yourself in her favour by every means in your power."

"Means!" repeated Craven; "what means are there that I have not tried to make her like me? I have attended to her far more than to any other girl of my acquaintance. I have encountered great danger, without shrinking, in her defence." (It is to be supposed that he alluded to the adventure of the mad dog.)-"I have had my picture painted on purpose to give her; and Heaven knows it is no joke sitting for one's portrait, bolt upright in a chair hour after hour, with all one's features stiff and prim, and obliged to stare hard at nothing, without daring to speak, or even to yawn.' Miss Craven thought that she had seen him do both an immense number of times, and also recollected that the artist had been very near giving up the portrait in despair, because he would not sit still; but she did not venture to remind him of this. "And besides," continued Sir Robert, "have I not fought a duel for her sake; am I not wounded; might I not have lost my life; only because Mr. Silverdale had a flower of hers, which, as Lady Seagrove has since told me, was not given as a mark of preference. I could have sworn it was not at the time. I knew it was only what that insolent, conceited fellow chose to say. I only wish I had him here this minute, to treat him as he deserves!" And Sir Robert brandished his clenched fist in his aunt's face, as if about to give her a specimen of the treatment he wished to make the unfortunate Silverdale undergo. "I know," he continued, "that the man thinks because he's a poet all the ladies must be in love with him. Certainly he has a most marvellous talent for twisting everything to suit his own views and wishes. I suppose that's what they call poetical licence. Ha! ha! ha! But, speaking of Florence, I am tired of shillishallying in this way. I had rather put the matter beyond all doubt at once; and shall seek an interview with her immediately on my recovery."

"Indeed, indeed," said Miss Craven, earnestly, "you had better wait a little longer."

No, no!" interrupted Craven, his obstinacy increasing in proportion to the opposition. 'Why should I wait? If she does not love me now she never will; and I am resolved either to marry her directly— that is, as soon as I am well- -or not at all."

"But Lady Seagrove," timidly suggested Miss Craven, "says that, notwithstanding all she can do, Florence still makes some objections, and until these can be overruled

"I'll tell you what," interrupted Sir Robert, "you are not going to overrule me; so you need not think it. Do you suppose I am under petticoat government still, or that I am not competent to decide for myself? If it was a gown or a bonnet I wanted to choose, I might ask your advice, but not about a wife. But I see how it is; you don't want me to have a wife yet, because you are afraid that when I am married you won't rule the roast as you do now; no more you will, I promise you. Even if Florence refuses me, which I think she will not be such a fool as to do, I shall make a point of getting a wife as soon as possible, if it's only to plague you!"