December 2, 1920] 



NATURE 



441 



The order of harilnoss is :- Diamond, iridium, 

 platinum, iron, arsenic, antimony, (^old-copper-silver, 

 aluminium, tin, bismuth, and lead-sulphur. (It is 

 probable thai arsenic and antimony were tested in a 

 1 rystalline state, in that respect differing from the 

 three metals above and the four below them.) 



'I'he order of ascending ciH-tTicients of expansion 

 is : — Diamond, arsenic, iridium, platinum, antimony, 

 Iron, bismuth, gold, copper, silver, tin, aluminium, 

 liad, and sulphur. Here the agreement is not so 

 1 lose as before. 



Doubtless coefficients of e.\pansiim themselves 

 depend partly on how far the mean range of tcin- 

 perature from which thev are calculated is removed 

 from the melting |K)int. l'"or strict comparison, what 

 are know n as "' corresponding temperatures " should 

 be taken. If this is done for co<-tficients of expansion 

 of gases, then the values become identical ; with 

 solids (or liquids) the coefficients would approach, but 

 never reach, uniformity. 



In practice engineers are bouml to consider arbitrary 

 temperatures which will affect their mi.xed materials, 

 Ijut a knt>wledge derived from comparison of physical 

 properties at corresponding temperatures would en- 

 able them to predict special ch.inges among the mixed 

 material which would occur when tem|)eralures rise 

 or fall. Kkc.in.m.I) <■. Dihkant. 



UnivCTsity College, Reading. 



The Hardening of Metals under Mechanical Treatment. 



li .ippi ars from an arlirli- \i\ Mr. Ilriii>.l A. Siiiitli 

 ill .\ArfRE of November iS, p. jXi, that the cause of 

 I he hardening of metals under mechanical treatmml 

 is still regarded as obscure. 



May I suggest, for the consideration of research 

 associations and others concerned, that all the pheno- 

 mena of plastic deformation, including hardening by 

 distortion, are aspects of what Osborne Revnolds 

 has called " dilatancy," and that this twentieth icn- 

 liiry is no time for random empirical experiments 

 I inducted without either guiding principles or clearly 

 ({"•fined objectives? 



Reynolds has shown that the densitv of a granular 

 -.olid must change when the soli<l is distortisl. There 

 is ample evidence that distortion alters the density 

 I'f metals, :md no verv valid reason for assigning lh<- 

 ..( (ompanying alteration of ■' hardness " (and other 

 liroperlics) to anything but a change in the patli-rn 

 iif the gr.-iins, i.e. to dilatancv. 



Systematic ex[«-rimental investigation can scarctiv 

 fail to have far-reaching results, and may even bridge 

 ilif gulf between mechanics and the more exact 

 •■ciences. J. Iwkn. 



12 Kdward's Road. Whitley Bav. 



N'orthumlierland, Novemlier 22 



Tube-dwellinx Phase in the Develoqment of the Lobster. 



Wiiit.sr thr (livilopment of thi- lobster from the 

 ScIiIzo|)(k1 sl.-ige onward to an in( h or a little more 

 is fairly well known, the great rarity of the stages 

 between that and 3 in. or 4 in. (second year) lias 

 often puzzled marine zoologists. For instance, only 

 once in many year* has a small loJ>ster of about 4 in. 

 t>een sren at St. .Andrews, and this example was 

 tossed amidst a vast qunntitv of d<^bris on shore after 

 1 violent storm. Prof. Princi-. Dominion Cornmis- 

 Moner of Fisheries for Canada, and president-elect of 

 ihe American Fisheries Soriely, who has inaugurated 

 manv important advances in scientific fisheries work, 

 tells n>e that Prof. Knighl. who has been investigating 

 the subject, finds that "after the pelagic stage the 

 voung lobster aprx'ars lo frequent shallow bav* and 

 maki- n di-finite burrow with two entrances, and it 

 sits on j»uard nf one, but if In danger es<-apes bv the 

 other. It is very quick in emerging, but Prof. 

 VO. 3^66. VOT.. T06I 



Knight and his assistant got 200 to joo in a bay in 

 Prince Edward Island. Now we know the reason of 

 our failing to capture these very small lobsters from 

 14 in. to J in. long. The dredge cannot secure them, 

 yet they must occur in countless millions in our 

 Canadian bays, since many more than 100,000,000 

 adults are taken in our waters for canning and the 

 live-lobster tr.ide in good years." Thus the rarity of 

 the little lobsters of the stage indicated is explained. 

 It is interesting that the adult, as shown by Dr. 

 H. C. Williamson, of the Scottish Fishery Board's 

 staff, has a similar fondness for cavities, which it 

 searches for with its antennae, and will even turn out 

 a weaker neighbour and seize its shelter. 



VV. C. .VIcIntosh. 



Contractile Vacuoles. 



1 ii.xvK just read W. Sliinpel's paper, ' Ueber die 

 Funktion der pulsierenden \acuole," to which Prof. 

 Bavliss kindly directed m\ attention in Nature of 

 November 18, p. 376. Stempel's idea as to how the 

 contractile vacuole works appears to differ funda. 

 mentally from my conception of its mechanism. He 

 regards it as a preformed organ of the cell, developed 

 lo eliminate the waste products of metabolism, these 

 products iH-ing intro<luced into the vacuole by the 

 •radiating canals which he endows with peristaltic action. 

 He furthi-r postulates the existence of non-return 

 valves b«-tween these radiating canals and the vacuole, 

 and also of one at the point of exit of the fluid to the 

 exterior. He considers that the evacuation of the 

 contents is effected by the osmotic pressure in the 

 vacuole, opening the valve and thrasting out the fluid, 

 bv the surface tensitni of the extruded drop, and by 

 the pressure of the protoplasm. He does not irKlicale 

 that the elasticity of the protoplasm or its tenacity 

 I'nters into the mechanism. .My suggestion may be 

 sunuiied up in the much simpler statement that the 

 contractile vacuole is a necessary development in the 

 protoplasmic semi-permeable gel wherever sufficient 

 soluble maleri.il .iciumulales, Ihe radiating canals 

 being formed bv I he elastic recovery of the gel after 

 rupture. Henry H. Dixon. 



School of Hol.-my, Trinitv Colb-ge, Dublin, 

 November 20. 



Leptocephalus of Conger in the Firth of Clyde. 



Is a nil III issue (vol. xii.. No. 2. July, K)2o) of 

 the Journ. Mar. Biol, .\ssoc. Mr. F.. Ford, in a 

 •■ Note on a Leptocephalus .Stage of the Conger," gives 

 ;« "summary of captures around the British Isles.'' 

 To the records there given, mav I add two from the 

 Firth of Clyde? 



(i) July, i<jo7: off Keppel Pier; 3 fms. ; length, 

 120 mm.'; depth, excluding fins, 8 mm.; a distinct 

 row of black spots .-ilong the lateral line. Taken 

 from the stomach of a s.iithe (Gadu!. v'xtenf), 



(2) March, i<)o8 ; .\rdnell Bay, 10 fms.; taken from 

 the stomach of a cod {d. dillarius) ; too much digested 

 to give anv details. RtcHARD l'!i.MlilR4T. 



Marine Biciloalral Station, K>-|)|)eI. Millport. 



Spiranthes autumnalis. 

 Sir Hkrmkkt Maxwki.i. will, I am sure, allow me 

 to make a little correction in his statement on p. 400 

 of N'ATfRK of November 25 ; it was not Sir Joseph 

 Jlooker, but Sir William' who in 1843 doubtfully 

 tiescribed a solilarv s()eiimen of Vrroniea Ictragotu 

 as a s|)ecios of the coniferous genuR Podocarpu*. 

 Oddlv enough, th<' plant was correctly described from 

 a flowering s|M'cimen in the same volume of Hooker's 

 " Irones " on a later plate. 



B. Datdos J.^ckson. 

 I.inni'.-in Society. Burlington House, 



London. \\',\, November 26. 



