1890.] 



On the Heat of the Moon and Stars. 



493 



I was able to observe Arcturus on the meridian in a clear sky, but 

 I obtained no effect. 



On March 25th, 1890, I tested the delicacy of this circuit with a 

 4-inch Leslie cube (black face) filled with boiling water at a distance 

 of 81f inches. The deflection due to the exposed area of about 

 4 square mm. was 50 mm. A new circuit, made of better materials, 

 gave a deflection of 180 mm. under the same conditions, and as this 

 seemed a good circuit, I used it last Easter with freshly silvered 

 mirrors. 



April 2nd, 1890. A perfect night, except a slight but persistent east 

 wind. The moon, not yet full, sent the index right off the scale 

 at once. It was too windy to make satisfactory observations on 

 stars. 



April 3rd. Perfect night. Wind very slight, N.N".E. Very dry. 

 Telescope tube and ether box covered with frost. Ether box so 

 cold that no separate oxygen was necessary. I balanced a paraffin 

 candle on a hedge at a distance of 93 yards, and found on moving the 

 telescope on and off with the slow motion screw a very constant 

 deflection of 55 mm. In this case the candle was so much out of 

 foe as that only about one-sixth of the rays fell on the disc, all the 

 rest passing by. I could not alter the focus sufficiently, nor could I 

 put the candle further away that night, but this was done the follow- 

 ing day. About 1 30 a.m. Arcturus was on the meridian. There was 

 not a deflection of J mm. in any of a number of very satisfactory 

 observations. Mars, low down in S.E., and Regulus and Saturn pro- 

 duced no effect either. 



On Good Friday, April 4th, I prepared a clear view up to a mound 

 250 yards away, where a mill once stood, by catting off the tops of 

 the hedges that were in the line. On this mound I placed a stand 

 carrying a beehive with a hole in the side. A candle placed in the 

 beehive would send its rays into the distant telescope without any 

 intermediate obstruction. A light paper shutter inside the beehive 

 was arranged so that it could be pulled to one side by a long piece of 

 cotton, and be allowed to fall back again so as to obstruct the radiation. 

 The exact distance from the candle to the mirror (obtained by chain- 

 ing) was 250*7 yards. During the day I moved the radio-micrometer 

 on its geometrical slide until the disc and the image of the beehive 

 were in the same plane. The image of the candle-flame, which was 

 about I mm. long, was then focussed upon the disc, and all the rays 

 which entered the telescope from any part of the flame were received 

 upon the disc. 



About 8 30 p.m., when it was fairly quiet, there being a slight east 

 wind, my niece, L. Wintle, kindly stationed herself on the mound out 

 of sight of the telescope, and at a signal either pulled or let go the 

 cotton. The telescope was pointed towards the candle the whole 



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