204 DESCRIPTION ET USAGE 
They were each taken in tow by a powerful « tug 
steamer ». But during the trial, thetow-rope was not per- 
mitted to be more tightly strained than was necessary 
in order to keep the ships broadside to the waves.— The 
ships were without masts : but sufficient iron ballast was 
placed on the upper deck of each to represent approxima- 
tively the dynamic effect of the masts, so that the « period» 
of oscillation in calm water was nearly what it would 
have been if they had been « ready for sea », namely 8": 
that is to say 4” for a single movement from starboard to 
port or from port to starboard. 
Both ships had been made to roll in calm water pre- 
viously, and the resistance of the water had been thus 
determined for each ship in the manner which you, as 
well as I, have pursued. 
In both of the ships, while rolling among the waves, 
the absolute angle was recorded by an observer who 
continually pointed à bar at the horizon in the manner 
which, you and ! have both adopted. In one of them 
it was also recorded by the automatic method which I 
think I have described to you, and which 1s also described 
by M. Reed in the article of which I send you a copy. 
{ will here only mention that it consists of a heavy « fly 
wheel » or wheel of great moment of inertia, very delica- 
tely suspended, so that it can revolve almost without any 
resistance by friction. It is nearly of 4 mêtre in diameter, 
and 400 Kg. in weight; it possesses à long axle of steel 
with hardened steel collars very tightly fitted on it at each 
end, 0,025 in exterior diameter; and these hardened 
ends rest on hard steel segments which are parts of cir- 
