105 
tube. This pendulum has another advantage, viz., that the 
steel rods and the zinc tube are so nearly the same in size that 
sudden changes of temperature affect all the parts nearly 
simultaneously, whereas in the mercurial pendulum the steel 
rod is much more quickly affected than the large mass of 
mercury ; the compensation therefore does not take place soon 
enough to prevent a small error in the clock’s rate. 
A letter by Mr. Dyer was read, relative to Dr. Rankine’s 
reply, inserted in the Proceedings of March 24. 
Mr. Dyer disavows all intention of unfairness towards 
Dr. Rankine, and states that although the brevity which it 
was necessary to observe in drawing up his abstract com- 
pelled him to give only detached passages, he conceived that 
the sense could not be considered to be perverted by reason 
of the omissions. He had always felt and expressed the 
highest regard for Dr. Rankine’s genius and learned researches. 
A Paper Avas read entitled “Note as to tAvo Events in 
the History of Steam Navigation,” by W. J. Macquorn 
Rankine, C.E., LL.D., P.R.S.,Hon. Member of the Society. 
(1.) An interesting Paper Avas lately read to this Society 
by Mr. Dyer, containing a history of a series of important 
events in the progress of Steam Navigation. 
(2.) It is to be regretted, however, that the author has 
noted either very slightly or not at all, Avhat appears to have 
been an event of paramount importance in the first adaptation 
of the double-acting cranked steam engine to drive a paddle 
Avheel. Before that adaptation Avas made, the success of all 
attempts at steam navigation, such as those of Jouffiay, 
Rumsey, Titch, Miller, and Taylor, &c., had been only 
temporary, because of the rudeness of the machinery for 
communicating motion from the piston to the shaft. 
(3.) That first adaptation Avas unquestionably accomplished 
by William Symington in 1801, as is proved by authentic 
documents Avhieh haA r e been published by Mr, Woodcroft in 
