356 Prof. Knoblauch on the Influence of Metals 
2nd. The imperfect transparency of the atmosphere. 
3rd. The screening effect of clouds of every thickness. 
4th. The difference in the absorbent power of the ground, &c. 
It is the variation in the temperature of the atmosphere thus 
produced which disturbs its equilibrium, and is the principal 
cause of all its great movements and changes; and it is surely 
therefore very desirable to possess an instrument which will enable 
us to estimate and record, however roughly, the actual amount 
and variation of this chief element in the science of Meteorology. 
It may be observed that the sun-gauge will equally well mea- 
sure terrestrial or night-radiation by distillation in the contrary 
direction, if a small quantity of liquid be left in the graduated 
tube. Or a special instrument of inverted form and action 
might be contrived, and continually exposed to the sky in the 
focus of a concave mirror, while being completely sheltered from 
the sun. 
Royal Mint, Sydney, New South Wales, 
May 14, 1857. 
(Mr. Jevons is evidently not acquainted with the interesting re- 
searches of Pouillet (Poggendorff’s Annalen, vol. xlv. for 1838) on 
the amount of the solar radiant heat falling on our globe. Pouillet 
gave a more perfect arrangement to Herschel’s Heliometer; and by 
observing the amount and rate of increased temperature which a 
quantity of water contained in a metallic vessel exposed to the direct 
sunlight underwent, and observing also the rate of diminution of 
temperature when the sun’s rays were cut off, he determined the co- 
efficient of absorption for heat of the atmosphere, and hence calcu- 
lated the thickness of a crust of ice which on the surface of the earth 
would be melted by the sun’s rays in a day, and that which would 
on the sun’s surface be liquefied by the solar heat.—Ep. ] 
XLII. On the Influence of Metals upon Radiant Heat. 
By H. Knosiavcn, Professor of Natural Philosophy in Halle*. 
i; 
\ \ 71TH respect to radiant heat, the metals have been hitherto 
regarded as adiathermanous bodies, and they have there- 
fore been employed as screens when it was necessary to cut off 
the calorific rays. With the thickness in which sheet-metal is 
found in commerce, this indeed might safely be done; but it 
decided nothing as to the real capability of metals to transmit 
radiant heat. This could only be ascertained by operating upon 
thin layers. 
To test this question, M. Knoblauch first made use of a gold- 
* Abstracted from Poggendorff’s Annalen, vol. ci. 1857. 
