TRANSACTIONS OF SECTION A. 521 



remain an integral portion of Section A, and though we acknowledge our weak- 

 nesses we claim to have also something to teach. 



I hope our proceedings this week may show that we can put aside observa- 

 tional detail and throw some light on the great and important problems with 

 which our science is concerned. 



Discussion on the Nehula surrounding Nova Persei, opened hy A. R. 

 HiNKS ivith an Exhibition of some Photographs from the Yerkes and 

 Lick Observatories. 



The following Papers were read : — 



1. New Solar Radiation Recorder. By Dr. W. E. Wilson, F.R.S. 



Professor Oallendar has used with his well-known electric recorder a form of 

 receiver for solar radiation which consists of two coils of platinum wire wound 

 on a mica frame. One of the coils is bright and the other black ; they are protected 

 from the rain by a glass shade. These two coils are the two arms of a Wheatstone 

 bridge, and the balance is upset by the sun warming the black coil more than the 

 bright. There are two disturbing factors in this form of receiver which are diffi- 

 cult to eliminate. First, the varying angle of the sun above the coils, which are 

 fixed horizontally; and secondly, the amount of radiation received from the entire 

 sky. This is constantly changing from the amount of cloud and haze present. 

 To overcome these difficulties I have had a receiver made in which the coils are 

 kept normal to the sun all day, and both coils are black and are sealed up in a 

 vacuum tube. One of the coils alone receives the solar radiation, and that only 

 from the sun, and a very small region of the surrounding sky. It was found that 

 with the Callendar form of ^receiver it was quite impossible to calibrate the 

 readings of the recorder with Angstrom's phyheliometer, but with the new receiver 

 the results can be accurately determined in calories per sq. cm. per minute. 



2. Search for ultra- Neptunian Planet. By Dr. W. E. Wilson, F.R.S. 



Last year at the meeting of the British Association at Glasgow Professor G. 

 Forbes, F.R.S., read a paper in which he pointed out the possibility of there bein" 

 an ultra-Neptunian planet. " 



In 1880 he made his first communication to the Royal Society of Edinburgh 

 and pointed out that as Jupiter and Neptune have each a distinct group of comets 

 whose aphelia lie close to their orbits, so in the same way there were two come- 

 tary groups which indicate that there were two planets beyond Neptune, one of 

 which was at about one hundred times the mean distance of the earth from the 

 sun. Dr. I. Roberts made a search for the planet in the position then computed 

 by Forbes, but with a negative residt. Since then Professor Forbes revised his 

 calculations, and considered some points which he thought greatly strengthened 

 his supposition in the reality of the unknown planet. He asked me to undertake 

 another search for him with my 24" reflector. This I gladly agreed to do, but I 

 found that the field of the reflector was so small, the num"ber of plates that it 

 would take to cover the field so large, and the weather of this country so hope- 

 less, that the work could not be done in a year. Sir David Solomons, Bart., 

 then kindly oflered to lend us a fine 6" portrait lense of i>8" focus. I had 

 a camera made for this to take plates 8^ x 6^, and it was bolted to the tube of the 

 24" reflector. In May 1901 we took with this lense a sufficient number of plates 

 to cover a region along the ecliptic each side of the theoretical place of the planet. 

 Last February a second series of plates were taken in the earlv mornings before 

 sunrise of the same positions, and these plates were superposed upon those of May 

 1901 and carefully examined for the planet, but I am sorry to say with a negative 

 result. The plates all got with the full aperture one hour's exposure, so that 



