On the Force of Percussion. - | aay 
_ Thus there exists no doubt upon the substance which 
colours the turquoise. If it was necessary to add to the facts 
already given, I would say, that having sent M. Vauquelin 
the same turquoises I had analysed, he found no particle of 
‘copper in them; lastly, I ascertained that, by pouring into 
a solution of muriate of lime phosphate of soda and some 
drops of muriate of iron at the maximum, a phosphate of 
lime and iron was obtained of a greenish blue colour: again, 
by decomposing the phosphate of soda by the muriate of 
iron at the maximum, we may obtain a phosphate of iron 
which is not white, as some chemists have said, but of a 
blueish green colour. 
The above reflections may not be very important ; but I 
offer them with the view of showing the possibility of imi- 
tating the colour of the turquoise, and as showing at the 
same time that iron, in several circumstances, may yield 
colours similar to those produced by copper. 
XXXVIIT. The Bakerian Lecture on the Force of Percus- 
sion. By Witt1am Hype Wottaston, M. D., Sec. 
ROS.* . 
Wauen different bodies move with the same velocity, it is 
universally agreed that- the forces which they can exert 
against any obstacle opposed to them are in proportion to 
the quantities of matter contained in the bodies respectively. 
But, when equal bodies-move with unequal velocities, the 
‘estimation of their forces has been a subject of dispute be- 
tween different classes of philosophers. Leibnitz and his 
followers have maintained that the forces of bodies are as 
the masses multiplied into the squares of their velocities (a 
multiple to which I shall, for conciseness, give the name of 
impetus), while those who are considered as Newtonians 
conceive that the forces are in the simple ratio of the velo- 
cities, and consequently as the momentum or quantitas motits, 
* From the Transactions of the Royal Society for 1806. 
Pa a name 
