498 



On the Heat of the Moon and Stars. 



[Apr. 24, 



two A bars are soldered to the lower ends of the copper wire arch, 

 two B bars are soldered to these and joined below. The A, B junc- 

 tions are then exposed in the radio-micrometer side by side, and so 

 are unaffected by general atmospheric influences, while as a star 

 passes from one to the other the effect of the star will be reversed. 

 On a quiet night the single junction works so well that I have not at 

 present tried the differential form. 



It is my intention to make observations from time to time when I 

 am able, but these, owing to my duties in London, can only be made 

 at uncertain intervals. 



[Note. — At the time that this paper was sent in I did not realise 

 that the larger figure that I obtained for the percentage trans- 

 mission of the moon's heat through glass, viz., 25, instead of about 

 17, as found by Lord Rosse, far from being of the nature of a dis- 

 crepancy, is in reality a difference which should be expected. Lord 

 Rosse made observations on the total heat only ; he did not localise 

 parts of the moon, as I have done. He found a greater propor- 

 tionate transmission at the full moon than at the quarters, viz., 17 

 at the full and 8 at the quarters. Now, taking elements in the 

 moon, I cannot think that this proportion can to any appreciable 

 extent depend on the altitude of the earth at the element, but it 

 should depend on the altitude of the sun there, for upon this the heat 

 received by the element depends. Now, in taking the full moon as 

 a whole, there are elements with the sun at all altitudes from 0° to 

 90° ; but those parts with the sun at the zenith are most favourably 

 situated to produce their effect on the earth, and thus the observed 

 effect, which is the result of all the parts, should show a percentage 

 transmission between that due to a zenith sun and a sun near the 

 horizon, which should also be the case with the moon at the quar- 

 ters or between the quarters and the full; but there is this difference, 

 as the moon approaches the quarters the effect of the parts on which 

 the sun is shining vertically becomes proportionately less and less, and 

 so while with a full moon the percentage transmission should 

 approach that due to an element with a vertical sun, with a half 

 moon the percentage should be more nearly that due to an element 

 with a rising or setting sun. 



Now my method of' observation of the moon at once gives the 

 means of finding the percentage transmission due to an element 

 with the sun at any altitude. The curve, fig. 4, shows that the centre 

 of the full moon does send a larger proportion through glass than 

 either limb, and, as it should do, a greater proportion than the inte- 

 gral result found by Lord Rosse. A single transit of the full moon 

 should, therefore, give data from which the integral result of the 

 moon in any phase could be calculated, and corresponding observa- 



