First, with cast-iron Armstrong shot, fired from Armstrong rifled guns, with charges one-eighth the weight of the shot

'Second, for flat-ended cylindrical steel charge, the charge being onefifth that of the shot, as in the case of the 300-pounder mentioned by Sir William Armstrong

'To test these results let us assume that the resistance of the combined structure, known as the "Warrior" target, with 44-in. facing, was equivalent to that of an unbacked 6-in. plate, and that of the "Hercules" target, with 9-in. facing, is equivalent to that of a 12-in. plate. This estimate, if not exact, cannot be very far from the truth; and, relatively, the resistance of one being four times that of the other, is the same as given by Sir William Armstrong. Then for cast-iron shot (formula 7) we find that a 264-pounder, with 33 lb. charge, will be required to penetrate the "Warrior" target (1), and a 1,500-pounder, with 187 lb. charge, to penetrate the "Hercules" target.

'Similarly, with steel flat-fronted shot, the "Warrior" will require an 80-pounder, with 16 lb. charge (2), and the "Hercules" target a 450pounder, with 90 lb. charge.

Now,

To be similar to the 300-pounder the 600-pounder should carry a charge of 120 lb. It is said to have been fired with 90 lb. looking to the fact that the shot is larger than that of the normal 450pounder in the calculation above, and will, therefore, require a greater charge, I am of opinion that if ever it is used against the "Hercules " target with a charge of 100 lb. of powder it will perforate the target (3). If 70 lb. of powder in a 600-pounder gun, as given in Sir William's letter, represents the limit of safe loading, then a somewhat larger charge still will be required; so that these calculations agree with and confirm the practical conclusion at which Sir William has arrived, that a gun carrying 120 lb. of powder will be necessary to penetrate that target, and this agreement in the result may lead him to be more disposed to accept the conclusion that the charges required to penetrate plates do not increase as the squares of the thicknesses of the plates, but in a higher ratio.

'Formula 8 gives for the penetration of the 300-pounder, with 601b. charge and steel shot, a thickness of 10 in. Now, Sir William

Armstrong states that that gun actually perforated the 9-in. facing of the "Hercules" target, doing some, if not much, damage to the backing. The agreement of fact and formula is as close as could be expected.

(1.) The 300-pounder, with a 150 lb. cast-iron shot, 10 in. diameter, penetrated the "Warrior" target with 40 lb. and 50 lb. charges. The shot of the 264-pounder, by assumption, would have been only 9 in. diameter.

(2.) The 80-pounder shot would be 63 in. diameter, so that this result agrees nearly with the experiments with Whitworth shell against the "Warrior" target.

'(3.) It was once fired with 70 lb. against an 11-in. unbacked plate, but the plate palpably gave way by transverse fracture, affording a strong confirmation of the views I have expressed on the mode of yielding of thick plates.

For the formulæ in this letter it will be seen that r=0·75 w nearly.'

The Fouling of Iron Ships.

The subject of fouling and the adhesion of barnacles to the hulls of iron vessels has been, since their first introduction, a source of trouble and of difficulty for which no effectual remedy has been applied. On enquiry at Liverpool as to the effect of fouling of iron vessels trading between that port and Calcutta, the author was informed by Captain Campbell, of the 'Kenyon,' that he had no trouble with his ship, as the plates were left perfectly clean after being a short time in the fresh water of the Hooghly. If this be the case, why not have docks or basins filled with fresh water at the different ports, into which vessels covered with mollusca might be floated, for the purpose of cleansing and removing the obstructions to which they are subject when built of iron ? It is an easy mode of getting quit of the nuisance, and that without injury to the plates.