492 



Prof. C. V. Boys. 



[Apr. 24, 



wind, but what there was was east. There was much dew, and by 

 9 p.m. the air had become filled with mist. Three observations on the 

 moon (three days past full) were taken, but owing to the low altitude the 

 actual amount of deflection was small. The regularity of the curves, 

 which were the only ones taken that night, is an indication of the 

 perfect quiet of the night. I examined also Vega, Altair, and « Cygni ; 

 there was certainly not a deflection of J mm. The index often did not 

 move mm. for several seconds. As this was a perfect night and 

 the dark side of the moon wa3 the advancing side, I made special 

 observations to see if any heat could be obtained from the dark part 

 on which the Sun had just ceased to shine, but not the slightest effect 

 was observed until the terminator itself met the disc of the radio- 

 micrometer. 



I had at this time to go to London, and so no more observations 

 were made until the early morning of October 31st, when I had re- 

 turned to observe the moon a few days before conjunction. The night 

 was windy after a wet day. At 3 30 a.m. the deflection on the limb was 

 25 mm. where it was greatest. As usual, it gradually decreased up 

 to the terminator. At 6 30 a.m., when the moon was higher and 

 better placed for a delicate test, I tried to observe the heat due to the 

 earth-shine, which was then very marked. Owing to the wind I was 

 unable to make a satisfactory negative observation, but it was cer- 

 tainly not 2 mm., and I believe not 1 mm. I have no record of 

 the deflection on the bright part. 



December 26th (5 30 p.m.). Venus very bright, but not at her best. 

 An equal area in the moon would produce an effect easily observable, 

 whereas a part of the moon large enough to produce the same light 

 would still more produce a measurable deflection. There was not a 

 deflection of ^ mm. I had, however, another circuit in the instrument 

 at this time which did not seem very sensitive. 



April 19th, 1889 (7 30 p.m.). Made many observations on Venus, 

 which had passed the position of greatest brilliancy. Sky clear, but 

 the night was windy, which kept the index moving over a space of 

 from 10 to 40 mm. Out of many transits observed, only two were not 

 interrupted by a violent gust of wind. In each of these cases there was 

 a deflection of from 2 to 3 mm. in the direction of heat, which may 

 have been real, but I do not place any reliance upon it. 



I was not satisfied with the delicacy of the apparatus and so made 

 a new circuit, and suspended it by a fibre 1/5750 inch in diameter. 

 With an exposed surface of about 4 square mm., illuminated by a 

 candle flame at a distance of 60 inches, this gave a deflection of 

 60 mm. 



As Mercury was unusually well placed in May, I took this circuit to 

 Wing, hoping to obtain effects from the most promising of planets. 

 Clouds, however, prevented Mercury from once being seen. Later on 



