10 
POPULAR SCIENCE REVIEW. 
observations, which throughout gave consistent results, was 
0*37 of a degree. To compare this effect with that from a ter- 
restrial source of heat, Prof. Smyth placed a Palmer’s candle 
14 ft. 9 in. from the pile, and took readings of the needle with 
the same alternations of exposure as he had adopted for the 
moon. Twenty-one readings gave a mean deflection of 0*77 
degrees ; so that the deduced heating influence of the moon 
appeared equal to half that shed by a candle to a distance of 
fifteen feet. 
Professor Smyth did not ascertain what this would be in 
terms of a recognised scale ; but M. Marie-Davy has since done 
so, using, however, not the mean of the two nights’ observa- 
tions, but that given by the first night’s, and assuming that the 
heating power of the candle used by him was not sensibly dif- 
ferent from that employed on Teneriffe. The first or full-moon 
night’s deflection was 0*25 of a degree, or a third of the candle- 
effect. Marie-Davy’s candle, at fifteen feet from his pile, gave 
a deflection to his needle amounting to 1 7 *3 divisions. A third 
of this would be 5 8 divisions, and this (the scale value of his 
needle being known to M. Marie-Davy) answered to 0*00075 
of a degree centigrade for the heating effect of the moon upon 
a body on the summit of Teneriffe. 
Passing over some negative results arrived at by Prof. 
Tyndall, in 1861,* from trials made upon the roof of the Eoyal 
Institution, without a condensing means beyond a large cone, 
and which were explained upon the hypothesis put forth by 
Buys Ballot, we next come to the experiments of the Earl of 
Kosse, for the making of which far superior means were avail- 
able than any at the disposal of previous investigators. One of 
the famous Parsonstown reflectors — the “three-foot” — was 
equipped specially for the work. The difficulty of compensa- 
ting for the effects of radiation on the anterior face of the pile 
compelled the adoption of two piles, f which were connected “in 
such a manner that a given amount of heat on the anterior 
face of one pile produced a deviation equal in amount and 
opposite in direction to that produced by an equal amount of 
heat on the anterior face of the other pile.” Small concave 
mirrors were used to still further concentrate the lunar rays 
collected at the focus of the great mirror. The galvanometer 
was of the construction introduced by Prof. Thompson to 
meet the requirements of the delicate currents employed in 
sub- Atlantic telegraphy. Instead of the needle pointing to en- 
graved degrees upon a circle beneath it, a mirror is attached to 
the suspending bar, and a lamp-flame is reflected from this 
upon a distant scale. In this manner, deflections imperceptible 
* “ Phil. Mag.” 4th ser. xxii. 377 and 470. 
t *See Plate and description. 
