ABRASION OF THE SURFACES OF SOLIDS. 
155 
REMARKS. — From the foregoing experiments it appears that there is a great deal of irregularity- 
in the results. 
Increase of pressure scarcely increasing the resistance. This may arise in some degree from the 
surfaces becoming condensed, and thus rendered less liable to abrasion. In some of the cases abra- 
sion had already commenced, but it was not convenient to pursue the experiment further. 
The soft woods present more resistance than the hard woods. 
Yellow deal on yellow deal being the greatest. 
Red teak on red teak the least. 
According to Mr. Knowles of the Navy Office, F.R.S., the weight of the Prince Regent of 120 
guns on the slips previous to launching, was 2400 tons ; which, divided by the area of the sliding 
surface of her bilge-ways (equal to 149,184 square inches), gives a pressure of36lbs. per square inch. 
But the weight of the Salisbury of 58 guns on the slips, according to the area of her bilge-ways, 
was 44lbs. per square inch. Now, by the foregoing Table, the average force required to put in 
motion the three different kinds of oak, under a pressure of 5 Gibs, per inch, is about |th of the 
pressure, which proportion prevails even as high as 6 cwt. per inch area : and by Table IX. we find 
that soft soap (the ingredient mostly used for diminishing the friction of bilge-ways under a pressure 
of 56lbs per inch,) gives about g—th of the pressure for the friction. Hence the angle at which a build- 
ing slip should be laid can be easily determined. Coulomb even makes 49lbs. per square inch, and 
27 th for the pressure for hogslard. 
The weight of the middle arch (of 151 feet 9 inches span) of the New London Bridge, together 
with the centres, is 4900 tons. This acting upon the surface of the striking wedges equal to 540 
square feet, gives a pressure of 140lbs. per square inch. The angles of inclination of the wedges are 
equal to 8 ° 45', and their surfaces are covered with sheets of copper well coated with tallow. On 
removing the check pieces, the wedges commenced gliding back slowly and uniformly by the gravity 
of the arch and centres, and the motion was checked and continued until the arch was left in 
equilibrio. 
Plate V. 
This apparatus was constructed both for brass and iron. The pivots were 
accurately turned, and the suspending- slings loosely hung. The total space 
passed over did not exceed four inches and a half. The cord was of the best 
sasli-line, and the pulley very sensible. The rigidity of the former and friction 
of the latter were accurately ascertained, by trials at different weights. The 
block was of cast iron accurately bored. The axle was allowed to have full 
play in the block, in order that no binding might take place. The space 
passed through was denoted by marks on the axle and block. The time by a 
seconds watch. 
An improvement was afterwards made in the apparatus, by substituting a 
roller of cast iron working in a block, and having a cord wound round its 
surface so as to allow of a descent of the moveable weight of 2 1 feet. 
x 2 
