1876.] Movement of the Glass Case of a Radiometer. 409 



III. " On the Placentation of the Lemurs." By Wm. Turner, M.B. 

 (Lond.), Professor of Anatomy, University of Edinburgh. 

 Communicated by Prof. Huxley, Sec. R.S. Received 

 February 21, 1876. 



(Abstract.) 



In the Introduction to this Memoir a description was given of the 

 observations made by M. Alphonse Milne-Edwards on the gravid uteri 

 of several genera of Lemurs. The author then proceeded to describe the 

 gravid uteri of six Lemurs which he had received from Dr. Andrew 

 Davidson, of Antananarivo, Madagascar, viz. Projnthecus diadema, Lemur 

 rufipes, and Indris brevicaudatus. He then summarized the conclusions he 

 had arrived at in the course of his dissections, and showed that the 

 placenta in these animals was diffused and presumably therefore non- 

 deciduate. The paper concluded with a discussion of the bearing of 

 these observations on the classification of the Lemurs, and on the theory 

 propounded by Haeckel of the descent of the deciduate mammals from 

 a primaeval root-form of Proshniae. 



IV. " On the Movement of the Glass Case of a Radiometer." By 

 William Crookes, F.R.S. &c. Received March 30, 1876. 



Daring the discussion which followed the reading of Prof. Reynolds's 

 and Dr. Schuster's papers at the last meetiDg of the Royal Society I men- 

 tioned an experiment bearing on the observations of Dr. Schuster. I have 

 since tried this in a modified form; and as the results are very decided and 

 appear calculated to throw light on many disputed points in the theory of 

 these obscure actions, I venture to bring a description of the experiment, 

 and to show the apparatus at work, before the Society. 



I made use of a radiometer described in a paper communicated to the 

 Society in January last. I quote the description from paragraph 184. 

 " A large radiometer in a 4-inch bulb was made with ten arms, eight of 

 them being of brass and the other two being a long watch-spring magnet. 

 The disks were of pith, blackened on one side. The power of the earth 

 on the magnet is too great to allow the arms to be set in rotation unless 

 a candle is brought near ; but once started it will continue to revolve 

 with the light some distance off:." 



This radiometer was floated in a vessel of water ; and four candles 

 were placed round it so as to set the arms in rotation. A mark was 

 put on the glass envelope so as to enable a slight movement of rotation 

 to be seen. The envelope turned very slowly a few degrees in one 

 direction, then stopped and turned a few degrees the opposite way ; 

 finally it took up a uniform but excessively slow movement in the direc- 

 tion of the arms, but so slow that more than an hour would be occupied 

 in one revolution. 



vol. xxiv. 2 II 



