166 . J. W. Fewhes — Deep-Sea Medusae. 



area it does not matter then whether the strip be made of a 

 single broad piece of platinum or of several narrow pieces 

 arranged side by side and connected in series. This however 

 is subject to the limitations mentioned in regard to the resist- 

 ance of the strip. The thickness of the strip does not occur in 

 the expression above ; we have supposed the strip flat and so 

 thin that the edges are only a very small fraction of the sur- 

 face, and the heat lost by conduction negligable ; as long as 

 these are true, the actual thickness of the strip is unimportant; 

 (t-t ) is the increase in the temperature of the strip above the 

 case due to the current passing through it ; for a particular 

 bolometer it is proportional to the square of the current. It is 

 this quantity most probably which regulates the strength of 

 current that can be used.* If we had two bolometers which 

 were identical in all respects except in the thickness and 

 blackening of the strips, we could apparently use currents in 

 them respectively strong enough to give the same value of 

 {t-t^) ; and if we made M the same for the two instruments, 

 the deflection produced on subjecting them to the same source 

 of radiation would be equal. The relative values of t-t for 

 different bolometers can only be determined by experiment ; 

 perhaps no great error would be made if we supposed them 

 equal for instruments which do not differ greatly in the ex- 

 posed area of their strips. 



Aet. XV. — Are there Deep-Sea Meduscef by J. Walter 



Fewkes. 



In a report on the Medusae collected by the " Albatross " 

 in 1883-84f I have already considered the question whether 

 there are zones of medusan life in the depths of the sea. I 

 have not, however, from the nature of that paper, written all 

 that may be said, even in the present condition of our knowl- 

 edge of the facts bearing upon it. It is hoped that the present 

 paper will, at least, point out the great interest attached to a 

 scientific answer to the question which is taken as the title of 

 this communication. 



A study of the fauna of the deep sea is of comparatively 



* It is possible that the total quantity of heat generated in the strip by the 

 current and communicated to the air and sides of the case may effect the limiting- 

 value of the current intensity. If so this would be an additional reason for mak- 

 ing the strip thin. 



f Report on the Medusas collected by the IT. S. Fish Commission Steamer 

 "Albatross" in the region of the Gulf Stream, in 1883-4. Annual Report Com. 

 Fish and Fisheries, 1884, pp. 927-977, Plates I-X, 1886. Many of the ideas here 

 presented are also noticed in this paper. 



