■On Curves generated by Images from Plane Mirrors. 69 



*ciously placed, and bad conducting surfaces, I have no doubt, 

 all objection, as regards want of air and excess of heat, might 

 be removed. 



The company, it appears to me, ought to look forward to 2k 

 time when, in the favourable season, at the beginning of our 

 winter, a voyage to the West Indies will be as commonly re- 

 commended to invalids requiring a mild winter climate, as to 

 Pisa, Naples, or Malta, at present. Were their steamers ven- 

 tilated as they might be, and kept of a mild temperature, having 

 the means of introducing warm air into the cabins as well as 

 cool air, they would be admirably fitted for conveying invalids ; 

 and the comfort afforded by them would be vastly increased, 

 and could not fail of being duly appreciated by the passengers ; 

 and, I will add, it may be for the interest of the company thus 

 to improve them, thereby giving them still greater advantages 

 than they at present possess over sailing vessels. 



Barbadoes, August 2. 1845. 



On some new and curious Curves, generated by the Images 

 reflected from Plane Mirrors, in a state of rapid rotation 

 around a fixed Axis. By Adam Andehson, LI^.D., 

 F.R.S.E., &c.. Professor of Natural Philosophy in the United 

 College, St Andrews. With three Plates. (Communicated 

 by the Author.) 



My attention having been lately directed to devise some new 

 contrivance for exhibiting, in a conspicuous and popular form, 

 adapted to a Class, the continuity of the sensation produced upon 

 the retina, when the impressions received by that organ from 

 well-illuminated objects, are renewed at short and successive 

 intervals, it occurred to me, among the different methods which 

 suggested themselves, that the object might be attained, in a 

 simple and effectual manner, by exposing a small mirror, in a 

 state of brisk revolution, to a pencil of the sun's rays, admit- 

 ted, through a small aperture, into a dark chamber. The me- 

 chanical contrivance to which I had recourse, for the purpose 

 of communicating a rapid angular motion to the mirror, con^ 

 sists of a wheel with 120 teeth, which acts on a pinion having 



