Intelligence and Miscellaneous Articles. 321 



instrument ; but in its present condition the heat radiated by a small 

 pan, containing a pint of water heated 30°, is quite perceptible at a 

 distance of three yards. A further proof of the extreme sensibility 

 of the instrument is obtained from the fact that it is able to detect 

 the heat radiated by the moon. A beam of moonlight was admitted 

 through a slit in a shutter. As the moon (nearly full) travelled from 

 left to right the beam passed gradually across the instrument, 

 causing the index to be deflected several degrees, first to the left and 

 then to the right. The effect showed, according to a very rough 

 estimate, that the air in the instrument must have been heated by 

 the moon's rays a few ten-thousandths of a degree, or by a quantity 

 no doubt the equivalent of the light absorbed by the blackened sur- 

 face on which the rays fell. — Proceedings of the Literary and Philo- 

 sophical Society of Manchester, March 11, 1863. 



ON THE MOTION OF VAPOURS TOWARD THE COLD. 

 BY THOMAS WOODS, M.D. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



In some of the late numbers of your Magazine I perceive there is 

 a discussion between Dr. Draper and Mr. Tomlinson as to priority 

 of the true explanation of the cause of the motion of certain volatile 

 substances towards the light. It is very remarkable how often 

 scientific men dispute priority of invention or discovery, and claim 

 it with the most sincere belief in the truth of their statements. 

 These disputes would form an interesting chapter in the curiosities 

 of scientific literature. I believe these claims arise from want of 

 sufficient attention on the part of the disputants to their true posi- 

 tion. For instance, one man devotes much time to a particular 

 pursuit, and arrives at certain broad principles which satisfy him. 

 Another, perhaps years after, happening to work out some part of 

 the same investigation in detail, publishes as an independent dis- 

 covery what might, when it is known, be deduced from the researches 

 of his predecessor, but which would for ever be a dead letter were it 

 not for his labour. The philosopher who was first in the field, how- 

 ever, is astonished (unjustly, I think) that any discovery should be 

 claimed ; and hence many of these disputes. 



Dr. Joule and myself were, I believe, somewhat in this predica- 

 ment with respect to the heat absorbed by the decomposition of 

 compounds * ; and I fancy such desagrements will constantly be 

 occurring, and not altogether without benefit to the public, as every 

 detail is so fully and prominently brought out. 



I make these remarks because, if Mr. Tomlinson had delayed 

 another month to publish his ideas on " the motion of camphor 



* Phil. Mag., 1856. vol. xii. 

 Phil Mag. S. 4. Vol. 25. No. 168. April 1863. Y 



