August io, 1905] 



NA TURE 



541 



takfii as representing the teaching given to metal- 

 lurgical students in America, and forms an interesting 

 stu'dv to those who wish to know something of the 

 much-praised methods in vogue there. Judging from 

 the contents of Prof. Lodge's volume, the methods 

 do not differ much from those in use in this country 

 and in other parts of the world. The assaying of gold 

 and silver ores is dealt with adequately, and there is 

 an interesting though incomplete chapter on the 

 metals of the platinum group, but the rest of the 

 third-vear work (the assay of bullion and of copper 

 and tin ores) is scrappy and of little value. The notes 

 for the fourth-year's work would also not be of much 

 help to students. For example, in the section on 

 cleaning mercurv, the student is recommended to wash 

 away soluble and light material with a stream of 

 water, and then to " decant off water and add a small 

 piece of potassium cyanide (poison), which ought to 

 clean it nicelv." The author seems to have some 

 misgivings as to whether base metals would really 

 be removed in this way, but the true nature of the 

 problem is nowhere stated, nor are the correct 

 methods of purification described. 



In the more valuable part of the book, the assaying 

 of gold and silver ores is discussed at considerable 

 length. The following differences between the in- 

 structions given to the student and those usually given 

 in England are noteworthy: — (i) In scorification the 

 slags are not cleaned by the addition of carbon after 

 the eye of lead is closed. (2) In cupellation, the forma- 

 tion of feathers of litharge is strongly insisted on. 

 (3) Beads from gold ores are parted by boiling three 

 times in nitric acid of different strengths. 



A large number of exact experiments in assaying 

 are described, and inferences drawn from them. Such 

 work is alwavs useful, but it is better not to put it 

 before students until it has been discussed. Some of 

 the inferences given can hardly be accepted, such, for 

 example, as that the presence of silver does not 

 diminish and that of copper does not increa.se the 

 cupellation loss of gold. -A word of protest may be 

 ■uttered against the low standard of draughtsmanship 

 in the illustrations. The scorifying tongs, depicted 

 twice, on pp. i ■? and ^S, are absolutelv startling. 



T. K. R. 



The Practical Photographer. Library Series. Edited 

 bv Rev. F. C. Lambert. No. iS, Gtim-bichromalc 

 I'riiitiug. Pp. xxiv + 64. No. 19, Floral Photo- 

 graphy. P]5. XX + 64. No. 20, Portraiture. Pp. 

 xxviii'+64. No. 21, Orthochromatic Photography. 

 Pp. XX + 64. No. 22, Figure Studie!:, Groups and 

 Genre. Pp. xx4-64. No. 23, .Summer Number. 

 Pp. 64. (London : Hodder and Stoughton, 1905.) 

 Price IS. net each. 

 The reputation of this excellent series of photographic 

 books is well maintained in the above-named additions 

 to this useful library. As in previous issues, each 

 volume is the work of numerous authors, and the 

 value of the series is that the information is given 

 by those who are at work at the various subjects, and 

 therefore more practical than theoretical. 



The illustrations, which are very numerous in each 

 number, are all of a high order of efficiency, and add 

 greatlv to the value and utility of the text. The 

 editor in each case contributes an interesting article 

 on the pictorial work of some photographer of note, 

 and those included in these numbers are, in the order 

 of the books given above : — Charles Moss, Mrs. 

 Cadby, Furlev Lewis, Harold Baker, William Raw- 

 lings, and F. J. Mortimer. .\n important feature of 

 each of these essavs is the reproduction of specimens 

 of their work. .As practical handbooks these new 

 volumes will be found very serviceable. 

 NO. 1867, VOL. 72] 



LETTERS TO THE EDITOR. 

 ]The Editor does not hold himselj responsible for opinions- 

 expressed by his correspondents. Neitlier can he undertaite 

 to return, or to correspond with the writers of, rejected' 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications .] 



Exploration of the Indian Ocean. 



Mr. Stanlev Gardiner, leader of the .Sladen Trust 

 Expedition for the exploration of the Indian Ocean 

 between Ceylon and the Seychelles, in H.M.S. Sealark, has 

 sent me the following short account of the progress of 

 the expedition up to the date of writing. The letter is 

 written from the Salomon .Atoll, Chagos Group, and is 

 dated June 4. A. Sedgwick. 



Trinity College, Cambridge, .August 4. 



•■ We came on board H.M.S. Sealark on May 8 at 

 Colombo. Weighing anchor the following evening we set 

 a course for Peros Banhos, the large N.W. atoll of this 

 group, but on the second day out appreciated the fact that 

 we were getting in for the commencement of the burst of 

 the S.W. monsoon. On May 14 we had reached a latitude 

 south of the Maldives, and commenced sounding in view 

 of the possible existence of a bank between this group 

 and the Chagos as indicated by the soundings taken by 

 the German Valdivia Expedition. I may say at once that 

 our soundings showed a depth of more than 2000 fathoms- 

 between the two groups. The depth increases from the 

 Maldives and Chagos towards the centre of the passage 

 between, but in this position there would seem to be a 

 broad flat, extending along the line of latitude with a 

 depth of 2000 to 2150 fathoms. Of course both east and 

 west the depth probably increases gradually to 25,000 

 fathoms or even more, but one obviously cannot build up 

 any views of a possible former connection of the Maldive 

 and Chagos Banks on such a slender basis. 



" On our way down we took samples of the sea-water 

 and of the plankton (pelagic fauna) at the surface and at 

 every 25 fathoms to 150 fathoms, using a wire with a 

 heavy weight at the end running over a measuring block 

 and clamping on the nets as each 25 fathoms ran out. 

 We also took a series of hauls with the Fowler and 

 Wolfenden closing nets, so as to get our wire into trim, 

 &c. The weather was dead calm with a moderate swell, 

 and generally our results were satisfactory. The Fowler 

 net, being opened at a certain depth and then hauled up 

 vertically to a lesser depth and closed, seemed more suit- 

 able for the conditions prevailing in this region than the 

 Wolfenden, which is opened and closed at the same depth, 

 being dependent on the drift of the ship, in the absence 

 of any deep-sea current, for what enters the actual net ; 

 heavy messengers, too, are essential for opening and 

 closing the nets. Of course these results on the depth of 

 pelagic animals have a value of their own, but our best 

 haul from a collector's point of view was that of a large 

 net, mouth one yard square, length about twelve yards, 

 made of strong mosquito cloth, ten meshes to the inch. 

 This net we let down on 1200 fathoms of wire and hauled 

 in as fast as our winch could take it. Unfortunately the 

 wire became tied up most abominably, but the comparison 

 of the contents of the tin with the collections made by 

 the Fowler net showed that the net itself must have 

 actually sunk to 600 or 700 fathoms. The presence in the 

 tin of a series of prawns Cone 6 inches long), a cuttle 

 fish, and many strong swimming jelly-fish suggests that 

 the use of this method of investigating the swimming 

 fauna (nekton) of the sea should yield valuable results. 



" On May iq we anchored at lie de Diamant. Peros 

 Banhos Atoll, but it became obvious in the next couple 

 of days that in the S.E. trade winds now prevailing in 

 this region, any thorough examination of this atoll, open 

 as it is to the S.E., w-ould be impossible. Accordingly 

 we moved on to the Salomon Atoll on May 22, coming 

 on shore to camp on the following day, selecting it as 

 being of small size (5 miles long by 3^ broad) and enclosed 

 on all sides, save for one passage to the north, by a 

 surface reef. While Cooper and I are collecting the 

 marine fauna and flora, and examining the reefs and land. 

 Captain Somerville and the officers of H.M.S. Sealark 

 are making a fresh chart of the atoll on a large scale, 



