260 DR. ROYSTON-PIGOTT. 



the action of stimulants. It is observed that the phospho- 

 rescent matter when extricated from the animal can be caused 

 to become luminous by agitation, by the action of fresh water, 

 of electricity, and of heat, as in the case of the luminous 

 matter of the Pennatulee, Medusae, of Pyrosoma, and of 

 other marine animals which are phosphorescent. 



5. The same matter becomes luminous when moistened 

 and agitated, even after it has been spread out and dried in 

 the air, or even if the phosphorescent organs have been 

 entirely dried without separating them from the mantle. 



6. Air and oxygen excite and maintain the light of the 

 Pholades for a long time during putrefaction ; carbonic 

 acid, on the contrary, extinguishes it. That air can re-illu- 

 minate it, whence one is led to believe that phospho- 

 rescence is a phenomenon which accompanies the oxidation 

 of the luminous matter. 



7. The light of Pholades is monochromatic like that of the 

 Beroes, Alcynoes, Ippopodiums, of the Pelagia, and of the 

 Eledones, and its band has a constant place in connection 

 with the lines of the solar spectrum. 



8. During the luminosity of the phosphorescent matter of 

 the Pholades there is no development of heat which can be 

 appreciated. This result has been arrived at after employing 

 the most delicate instruments, to wit, those very same ther- 

 mo-electric piles and the same galvanometer with which 

 Melloni succeeded in determining the small amount of heat 

 furnished by the lunar rays. 



On the Present CoNniTiON of English Object-Glasses 

 as regards Defining Power. By Dr. G. W. Boyston- 

 PiGOTT, M.A. Cantab., Fellow of the Cambridge Philo- 

 sophical Society, the Royal Astronomical and Microscopi- 

 cal Society, Member of the Royal Institution, Royal Col- 

 lege of Physicians, and late FelloAv of St. Peter's College, 

 Cambridge. 



The very considerable improvement that has taken place 

 in the construction and performance of the best English 

 glasses during the last two or three years leaves in the 

 minds of many persons a conviction that nothing further 

 need be done in this direction. Even three years ago Mr. 

 Wenham pronounced them perfectly corrected ; but the 

 great advance made since that time has in some measure 

 modified this opinion. Mr. Wenham's opinion was thus 



