B. DAYDON JACKSON ON AN IMMERSION PARABOLOID. 209 



being about 110°, a result I have not been able to attain so satis- 

 factorily by any means previously employed. There is no loss of 

 light by reflection from the lower surface of the glass, since the 

 rays pass almost in straight lines from the curved sides to the 

 focus. The ordinary test diatom slide, when mounted dry on the 

 cover, as usual, present a curious appearance, the field being dark 

 with a small spot of orange-brown light, occupying about one-fifth 

 of the diameter, the spherules, however, being shown distinctly. I 

 have not been able as yet to use this illuminator with higher powers, 

 the fog surrounding the object unpleasantly. 



My acknowledgments for the instrument are due to Mr. Ack- 

 land, who calculated the curve, and made the paraboloid ; and to 

 Mr. Suffolk, who obligingly placed all the data in his hands at the 

 disposal of the first -named gentleman. 



NOTICES TO MEMBERS. 



The Annual General Meeting of the Club will be held at University College, 

 on July 28th, at Eight o'clock, for the Election of Officers, Sfc. 



Members are requested to deliver to the Secretary the titles of papers and 

 communications which they intend presenting to the Club at the Ordinary 

 Meetings during the succeeding six months. 



