499 
of Edinburgh^ Session 1865-6G. 
probable that the actual motion of the cable lengthwise through 
the water can affect this result much. Thus, the velocity of settling 
of a horizontal piece of the cable (or velocity of sinking through 
the water, with weight just borne by fluid friction) would appear 
to be about *8 of a mile per hour. This may be contrasted with 
longitudinal friction by remembering that, according to the previ- 
ous result, a longitudinal motion through the water at the rate of 
1 mile per hour is resisted by only weight of the por- 
tion of cable so moving. 
These conclusions justify remarkably the choice that was made 
of materials and dimensions for the 1865 cable. A more compact 
cable (one for instance with less gutta percha, less or no tow round 
the iron wires, and somewhat more iron), even if of equal strength and 
equal weight per mile in water, would have experienced less trans- 
verse resistance to motion through the water, and therefore would 
have run down a much steeper slope to the bottom. Thus, even 
with the same longitudinal friction per mile, it would have been 
less resisted on the shorter length; but even on the same length 
it would have experienced much less longitudinal friction, because 
of its smaller circumference. Also, it is important to remark that 
the roughness of the outer tow covering undoubtedly did very 
much to ease the egress strain, as it must have increased the fluid 
friction greatly beyond what would have acted on a smooth gutta 
percha surface, or even on the surface of smooth iron wires, pre- 
sented by the more common form of submarine cables. 
The speaker showed models illustrating the paying-out machines 
used on the Atlantic expeditions of 1858 and 1865. He stated 
that nothing could well be imagined more perfect than the action 
of the machine of 1865 in paying out the 1200 miles of cable 
then laid, and that if it were only to be used for paying out, no 
change either in general plan or in detail seemed desirable, except 
the substitution of a softer material for the “jockey pulleys,” by 
which the cable in entering the machine has the small amount of 
resistance applied to it which it requires to keep it from slipping 
round the main drum. The rate of egress of the cable was kept 
always under perfect control by a weighted friction brake of Appold’s 
construction (which had proved its good quality in the 1858 Atlan- 
tic expedition) applied to a second drum carried on the same shaft 
