14 NATURAL SCIENCE. july. 



Porto Grande, St. Vincent ; of Ngaioa Bay in the Fiji Islands ; and 

 of Nares Harbour in the Admiralty Islands ; Kerguelen Island was 

 partially surveyed, and positions selected for the observations of the 

 transit of Venus ; Heard and MacDonald Islands were sketched in as 

 the ship passed ; the extent of the coral bank surrounding the 

 Bermudas was determined, and a new coral bank to the south- 

 westward of that group discovered ; and so on. 



7. Observations for the determination of the set of the currents 

 in the ocean, when circumstances were favourable, were accurately 

 obtained (i) by anchoring a boat by means of the dredge, or trawl, 

 and (2) by lowering a drag to various depths, and determining the 

 drift of this drag from the boat at anchor. This is the only way in 

 which these observations can be accurately made, and, so far as is 

 known, the "Challenger" Expedition alone has adopted these means. 



T. H. TiZARD. 



II.— OCEANIC CIRCULATION. 



The series of memoirs on the physics and chemistry of the 

 voyage of H. M.S. "Challenger" is fitly concluded by an Appendix 

 dealing with the circulation of waters in the great oceans, by Dr. 

 Alexander Buchan. Since this has only just been published, we give 

 a more detailed account than is required by the other memoirs. This 

 report consists primarily of sixteen maps, on which are exhibited the 

 distribution of temperature and salinity at various depths, so far as 

 made known to us by the observations of the " Challenger " and of a 

 number of subsequent deep-sea expeditions. Our information is 

 unfortunately still insufficient to allow of the construction of maps 

 showing salinity at any level except the surface ; but Dr. Buchan has 

 drawn very complete isothermal charts of the mean temperatures at 

 the surface, at every hundred fathoms up to 1,000, and at 1,500 

 fathoms ; and more isolated observations are charted for tempera- 

 ture at 2,200 fathoms, and for temperature and salinity at the bottom 

 where the depth exceeds 1,000 fathoms. Some forty pages of letter- 

 press are devoted to a general account of the temperature phenomena 

 disclosed by the maps, and of the probable oceanic circulation 

 suggested by them. 



It is scarcely possible to over-estimate the scientific value of the 

 information set forth in this report, which may be regarded as the 

 first serious attempt to represent as a whole the distribution of 

 temperature in the great water-masses of the globe. Nearly thirty 

 years ago Dr. Buchan published his classical memoir on the distri- 

 bution of atmospheric pressure over the earth's surface, and it cannot 

 be doubted that the present work will take a place aniongst oceano- 

 graphers similar to that occupied by the former amongst meteorologists. 

 As Dr. John Murray points out, the results as far as now ascertained 

 show the urgent need for further exploration in the Southern Ocean, 

 the western half of the South Atlantic, and the Pacific from about 



