6 
POPULAR SCIENCE REVIEW. 
inches in diameter, and one bulb of the thermometer, previously 
blackened to increase its heat-absorbing power, was mounted at 
the focus. The reflector was opposed to the light of the full 
moon, and, to quote the observer’s words, “the liquid began 
immediately to sink, and in half a minute was depressed eight 
degrees, when it became stationary. On placing a screen 
between the mirror and the moon, it rose again to the first level, 
and was again depressed on removing this obstacle. I repeated 
this experiment several times to satisfy myself, and some of my 
friends who happened to be present, that there was no fallacy 
in the conclusion of its being a positive proof of the calorific 
power of the lunar rays, and at the same time affording an 
evidence of the great delicacy of the instrument.”* The eight 
degrees here indicated were not those of any recognised thermo- 
metric scale, but mere arbitrary divisions upon the tube, about 
a millimetre apart. Within a year or two Pictet repeated 
Howard’s experiment, using a similar thermoscope, but his index 
remained unmoved under lunar influence ; if it altered at all, it 
gave an indication of cold. Prevost, reporting these results, 
pointed out that a mirror apparently reflects cold when exposed 
to the clear sky, because it intercepts the earth’s warmth, and 
leaves the thermometer free to radiate its heat towards the sky. 
He thought the same effects would be produced whether the 
reflector be turned to the moon or to any other part of the 
heavens; and he suggested the desirability of experimenters 
making this test a part of their lunar thermoscopic observations. 
Further, he remarked that heat might be experienced occasion- 
ally, on fine summer nights for instance, for then the upper air 
is warmer than the lower. f Howard’s strongly manifested 
warmth may have come from this source ; possibly Montanari’s 
also, and some detected byFrisius in 1781. Professor Volpicelli, 
in some historical notes on lunar thermometry, mentions certain 
researches by a Mr. Watt, which seemed to confirm Howard’s ex- 
perience. This was Mr. Mark Watt, a member of the Wernerian 
►Society. His experiments, besides being rather unphilosophical, 
hardly bear upon the point : they refer rather to some supposed 
attractive and repulsive actions exercised b} 7 the moon’s light upon 
little discs of metal mounted at the ends of a balanced bar.J 
There is mention of heat from the lunar rays, but it is am- 
biguous. 
The experiments so far prosecuted, while they evidenced the 
anxiety of physicists to settle the point at issue, only proved 
the inefficacy of the means which, in expansion thermometers, 
they possessed for the purpose. But presently came a revolu- 
• “ Silliman’s Journal,” vol. ii. p. 329. 
t “ Bibliotheque universelle,” xix. 36. 
| “ Edinburgh New Philosophical Journal,*’ xix. 122. 
