CVI ROYAL SOCIETY OF CANADA 



April the 8th, a communication from Prof. Campbell, director 

 of the Lick Observatory, was received, relating to the method employed 

 by Perrine to determine the non-polarity of light from condensations 

 in nebula of Nova Persei, observed a few days before this date. It was 

 explained that Perrine had interposed a double prism 3 inches in front 

 of the photographic plate, and had rotated the prisms without getting 

 polarization effects which should have shown if the light was reflected 

 and not directly radiated. 



The paper of the evening was by Prof. G. F. Hull, of Dartmouth 

 College, on " The Pressure of Light in its application to Astronomical 

 Problems." It was pointed out that Maxwell had shown that according 

 to the electro-magnetic theory of light, light should exert a pressure 

 on unit surface equal to the energy of one nnit of volume, divided 

 hy the velocity of light. This magnitude, as calculated by him, was 

 so small that little hope was held out of it ever being experimentally 

 observed. Eecent experiments by Dr. Hull and Professor Nichols 

 had given decisive demonsitration of the existence of this minute force, 

 the actual force observed agreeing with the calculated result to within 

 5 per cent. A brief description of the appairatus was given. It was 

 shown that on a body sufficiently small, the pressure due to the light 

 of the sun would be greater than gravitative attraction, but there is a 

 limit to this smallness. It was also remarked that velocity due to 

 light pressure might be great, but it could not equal the velocity of 

 light itself. 



At the meeting of the 22nd April, Mr. Arthur Harvey made a few 

 remarks regarding the value of the hand method of mapping the con- 

 stellations. The President reported that the seismograph at the observa- 

 tory had recorded a severe earthquake shock, accompanied by a sharp 

 electrical disturbance on April 18th, at 4.38 p.m. The origin of the 

 disturbance was afterwards found to be in Guatemala, the shock tak- 

 ing place there about eleven minutes before it was recorded in Toron- 

 to, and as the distance separating these two points is about 1,800 

 miles, 11 minutes would represent a velocity of 2| miles per second 

 approximately. John A. Paterson, M.A., K.C., presented a paper 

 idealing with " The Apex of the Sun's way." Tlie different methods of 

 determining the direction of the Sun's motion in space were comment- 

 ed upon and the most modern results presented, indicating apparently 

 that the solar system is moving towards the vicinity of Vega, a bright 

 star in the constellation Lyra, at the rate of about 10 miles per second. 



May 6th, Mr, P. L. Blake, of the Observatory staff, described the 

 transit instrimient, also the chronograph and other instruments in 

 use at the observatory for measuring and recording time. It was 

 remarked that the mercurial pendulum is in use at the observatory in 



