171 
of Edinburgh, Session 18 ( 39 - 70 . 
also be ascertained by means of an instrument on the principle of 
Leslie’s differential thermometer, one bulb of which would be placed 
at the bottom of the glass funnel, while the other would be pro¬ 
tected from the rain. In this way the differences of temperature 
would be constantly shown bjr means of a single instrument. 
The following Gentlemen were elected Fellows of the 
Society :— 
James Watson, Esq. 
The Hon. Lord Mackenzie. 
Monday, 6 th June 1870. 
Dr CHRTSTISON, President, in the Chair. 
The Secretary read the following letter from Professor W, 
J. Macquorn Eankine :— 
Diagrams of Forces in Framework. 
To the Secretary of the Royal Society , Edinburgh. 
Sir, —As Mr Clerk Maxwell, in a paper lately published in the 
Transactions of this Society, has done me the honour to refer to 
me as having been the first to show how to combine in one diagram 
a system of lines representing the directions and magnitudes of all 
the forces acting in a given frame, I wish to put on record, in the 
Proceedings of the Society, the time and manner of my first publi¬ 
cation of the method in question. It was in the year 1856, in a 
lithographed synopsis of lectures which I delivered in the Univer¬ 
sity of Glasgow, entitled u Mechanical Laws, Formulas, and 
Tables.” Copies of that synopsis were distributed to the students 
of my class, and to a few men of science. 
I beg leave herewith to send for presentation to the Society a 
copy of the first part of that synopsis, and regret that at present I 
am unable to make up a complete copy. The construction of 
diagrams of forces for unbraced frames is shown at p. 7, and for 
braced frames at p. 8. 
The next publication of the method took place in 1857, in the 
