1875.] On the Cruise of H. M.S. < Challenger.' 33 



The President expressed his regret, which would be shared by the 

 Society, that intelligence had been received by the Admiralty of the 

 decease, at sea, of Dr. von Willemoes-Suhm, a distinguished young 

 Naturalist attached to the Scientific Staff of the ' Challenger ' Expedition. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



A direct-vision compound prism by Merz, the gift of Mr. Gassiot, was 

 presented to the Society. It is regarded by the maker as one of remark- 

 able excellence, and is composed of a central prism, of large angle, formed 

 of peculiarly heavy lead glass, with opposed prisms of crown glass 

 cemented to its two faces. It is capable of taking in a pencil of rays of 

 28 k lines in width. The indices of refraction, in the heavy glass, of Praun- 

 hofer's lines 0, D, E, P are given by M. Merz as follows : — 



C n =l-7389. 

 D w =l-7513. 

 E n =l-7621. 

 P n = 1-7723. 

 Hence the dispersion is almost double that of ordinary flint glass. 

 The following Papers were read : — 



I. " Report to the Hydrographer of the Admiralty on the Cruise 

 of H.M.S. < Challenger ' from June to August 1875." By Prof. 

 Wyville Thomson, F.R.S., Director of the Civilian Scientific 

 Staff on Board. (Published by permission of the Lords of the 

 Admiralty.) Received October 28, 1875. 



[Plates 3-7.] 



Hilo Hawaii, August 18, 1875. 

 Sir, — The ' Challenger ' left Yokohama on the 16th of June, and ran 

 an easterly course between the parallels of 35° and 40° north latitude, 

 as far as the meridian of 155° east. We then turned nearly directly 

 southwards and reached Honolulu on the 27th of July. The weather 

 throughout was sufficiently favourable ; shortly after leaving Yokohama 

 there was a good deal of swell, which interfered somewhat with our 

 dredging-operations and caused the loss of a good deal of time ; we esta- 

 blished, however, 24 observing stations, at each of which most of the de- 

 sired observations were made. On the 17th of June we sounded in 1875 

 fathoms, with a bottom of bluish-grey clay and a bottom-temperature of 

 1°'7 C, 40 miles to the south-east of JSTo-Sima Lighthouse. The trawl was 

 put over, and it brought up a large quantity of the bottom, which showed 

 the clay was in a peculiar concretionary state, run together into coherent 

 lumps, which were bored in all directions by an Annelid of the Aphrodita- 

 cean group. In many cases the Annelids were still in the burrows. 

 Among the clay there were large lumps of grey pumice. The trawl con- 

 tained several fishes (belonging, as usual, chiefly to the family Macruridae) 



VOL. XXIV. D 



