488 



Prof. C. V. Boys. 



[Apr. 24, 



within 100 yards, and these are screened ojf by trees. The only 

 objection is the rather long railway journey, which prevents isolated 

 observations at odd times, and makes special observations of temporary 

 phenomena very inconvenient. 



The column is bolted down to a mass of about 2 tons of concrete, 

 bedded upon the rock. The protecting house is made of wood and 

 galvanised iron, and rests by four grooved wheels on rails made of 

 gas-pipe, so that it can, when its own holding-down bolt is un- 

 screwed, be pushed away so as to leave the telescope clear. The 

 door lifts off and rests against two posts in one of the borders near. 

 The figure will be sufficient to make every part, except minor details, 

 perfectly clear. I think it will be best to describe the observations 

 in the order in which they were made. 



I began observations on the 6th September, 1888. The night was 

 clear, but there was a gentle wind from the S.W., which produced an 

 uncertainty in the position of the zero of a few millimetres. To keep 

 off the wind I pulled the house over the telescope and looked east. 

 Capella and Regulus gave no indication (11 20 p.m.), certainly not 

 ^ mm. There were several good negative observations. An earwig 

 then began to climb up the delicate circuit of the radio- micrometer, 

 and as it was windy I left, after first removing the circuit. 



September 7th. To keep earwigs, of which there were an enormous 

 number this year, and spiders from coming into the radio-micrometer, 

 I placed in the diaphragm tube some cotton-wool which had been 

 soaked in creosote. Thunderstorm in the day; at night wind north 

 and cold. Dew on the telescope. Observed many stars up to 3 a.m., 

 including Altair, Arcturus, a, /3, and 6 Orionis, and Capella. No deflec- 

 tion of as much as 1 mm. Wind prevented greater accuracy. About 

 3 a.m. some fleecy clouds passing produced strong effects of heat long 

 before the star showed any diminution of brightness to the eye. A few 

 leaves on the top of a distant tree produced an effect of about 60 mm. 

 of heat. 



September 11th. A new moon, just above the horizon (about 4°), 

 produced, the instant the image of the limb met the disc, a rapid 

 movement of about 30 mm., which gradually declined to about half 

 when the terminator was reached, after which the deflection at once 

 fell to nothing. There was no indication of heat from the dark part 

 of the moon. The night being good, I was out till dawn, and tried 

 all the bright stars in Pegasus, Andromeda, and Orion, as well as 

 Aldebaran, Castor, Capella, and Saturn. No result from any of 

 them, certainly not \ mm. 



September 12th. At 5 30 p.m. the moon, first quarter, was low down 

 in the south. Observations at 5 50 and at 5 54 in the daylight 

 showed deflections at the limb of 125 and 120 mm., which, as before, 

 became less towards the terminator, where they vanished. 



