198 



NATURE 



[July 2, 1891 



Nearctic regions of Mr. Sclater and Mr. Wallace, I should 

 certainly not have suggested to Prof. Heilprin a new name for 

 that combination. Anyone looking to the passage (Proc. Zool. 

 Soc, 1868, pp. 314, 315) in which Prof. Huxley defined his 

 "Arctogsea" — a name to which, let me say, I have not the 

 least objection — will see that it signifies that part of the world 

 which is not "Notogaea," and therefore includes the Ethiopian 

 and Indian regions of Mr. Sclater, whereas my "Holarctic" 

 region expressly excludes them, and is therefore a very different 

 thing from " Arctogsea " in its true sense. 



Alfred Newton. 

 Magdalene College, Cambridge, June 12. 



Force and Determinism. 



In your issue of March 12 (vol. xliii. p. 491), Dr. Oliver J, 

 Lodge characterizes as " perfectly correct " the statement *' that, 

 although expenditure of energy is needed to increase the speed 

 of matter, none is needed to alter its direction." I have looked 

 in vain for some notice of this apparently strange doctrine in 

 your subsequent issues, with the exception that Prof. C. Lloyd 

 Morgan (April 16, p. 558) objects that the direction of motion 

 cannot be changed by purely metaphysical means, or will-power. 

 But passing over this rather important and interesting point with 

 only the observation that Sir John Herschel thought diffprently 

 — thought, in fact, that "without the power to make some 

 material disposition, to originate some movement, or to change, 

 at least temporarily, the amount of dynamical force appropriate 

 to one or more material molecules, the mechanical results of 

 human or animal volition are inconceivable" {Fortnightly 

 Review, July i, 1865, vol. i. p. 439) — I desire to call a 

 moment's attention to the first statement alluded to. 



Dr. Lodge admits that "expenditure of energy is needed to 

 ncrease the speed of matter." But, as a matter of fact, is it not 

 very difficult, if not indeed practically impossible, to change the 

 direction of a moving body without affecting its speed? "A 

 force at right angles to motion does no work," says Dr. Lodge. 

 Let us examine this statement for a moment. Let a body be 

 moving in the direction ato b with a speed sufficient to traverse 

 the distance in one unit of time. Then let a force be applied to 



the body at a, at right angles to the direction of its motion, 

 sufficient, if acting alone, to carry the body to d in the same unit 

 of time. By the composition of forces, the body, at the end 

 of the unit of time, would, therefore, be found at c. But the 

 distance ac is greater than ab ; and as, by the interposition of a 

 force at right angles to its motion, the body has thus traversed a 

 greater distance in the same time, has not its speed, as a matter 

 of fact, been increased ? and is not this increase of speed actual 

 work? and does not this work require actual energy to 

 perform it ? Evan McLennan. 



Brooklyn, Iowa, U.S.A., June 9. 



I AM glad to see my statement called in question, and hoped 

 that it would have aroused more antagonism than has yet been 

 expressed ; because I do believe that it has important psycho- 

 logical or metaphysical consequences, and should therefore 

 either be repudiated by physicists or after due discussion be 

 accepted by non-physicists. 



With regard to the special objection raised by Mr. McLennan, 

 it may be sufficient to remark that, in his diagram, ac is the 

 line of motion, ad the direction of the force, and that ad is not 

 at right angles to ac. His difficulty seems to be the one that 

 some people always feel with regard to the use of infinitesimals 

 in general. He must remember that his diagram will not apply 

 NO. 113 1, VOL. 44] 



to the case of curvilinear motion unless the impulses contem- 

 plated are momentary and infinitesimal. 



Oliver J. Lodge. 



The Scorpions at the Zoo, 



Your contributor of the notice, published in Nature on 

 June 18 (p. 163), on the contents of the Insect-house at the Zoo, 

 who laments the unfortunate circumstance that the scorpions 

 there in captivity remain unnamed, may be glad to learn that 

 these creatures may be easily identified, and, w^ith a little dex- 

 terity, fearlessly handled. 



During a recent visit to this house, the keeper obligingly 

 showed me the two Egyptian scorpions, one of which— the 

 black individual with the thick tail — was easily recognizable as 

 Prionnrus crassicauda, Oliv., a tolerably common North 

 African and Syrian form. 



To the other, however, I could not so readily assign a name ; 

 partly ovving to its partial concealment, and partly to the fact 

 that critical inspection is required to distinguish between the 

 species of the genus to which it belongs. It appeared, never- 

 theless, to be a specimen of ButJms europceics, Linn., the com- 

 monest of all the Mediterranean scorpions. But my attempt 

 to verify this point by closer examination was immediately 

 frustrated by the keeper ; who, evidently thinking that I was 

 qualifying for incarceration in Bedlam, hastily interposed when 

 I stretched out my hand to pick up the noxious animal. 



The third scorpion I did not see ; but doubtless it is a 

 specimen of one of the species of Euscorpius. This, too, can 

 be easily named, no doubt ; but it will be necessary to handle 

 the specimen in order to be certain on the point. 



I would warn your contributor not to be too sanguine of the 

 permanence of the amicable relations that appear at present to 

 be established between these three Arthropods. If the supply 

 of dead mice runs short, there will, of a surety, soon remain 

 nothing but a few fragments ol Etiscorpitis. Such thoroughgoing 

 cannibals are not likely to be squeamish, when a member of 

 another genus is before them. 



In conclusion, some of your readers may be interested to know 

 that the spider referred to as Lycosa portosantatta — which, by 

 the way, should be styled Tarantula maderiana — is a very near 

 ally of the famous and historical Tarantula of Italy ; and that 

 the hairy Brazilian monster, the so-called Mygale, who squats 

 under a broken flower-pot in the next cage, has no more claim 

 to the title Tarantula than any other Arachnoid with a formid- 

 able aspect. R. I. PococK. 



Natural History Museum, June 18. 



Cetaceans in African Lakes. 



With reference to Mr. Sclater's inquiry (Nature, June 11, 

 p. 124) as to the occurrence of porpoises in the Victoria Nyanza, 

 the following extract from Bernier, who wrote about 230 years 

 ago, will probably prove of interest. 



I may add that in another passage Bernier gives further in- 

 formation regarding the sources of the Nile. 



It would seem from the passage quoted that the occurrence of 

 a Cetacean in the Abyssinian sources of the Nile was probably 

 known to early travellers, and, like the occurrence of diamonds 

 in other parts of Africa, cannot be regarded as a new discovery. 



Science and Art Museum, Dublin, June 22. V. Ball. 



An Armenian named Murat and a Mogul who came as am- 

 bassadors from the Christian King of Ethiopia {i.e. Abyssinia) 

 to Aurungzeb shortly after his accession to the Mogul Empire, 

 in 1659, told the French physician Bernier, who then resided at 

 the Mogul's court, " that the Nile had its origin in the countrey 

 of Agaus, that it issued out of the earth by two springs 

 bubbling up near to one another, which did form a little lake of 

 about 30 or 40 paces long ; that, coming out of this lake, it did 

 make a considerable river ; and from space to space it received 

 small rivers increasing it. They added that it went on circling 

 and making as 'twere a great isle, and that afterwards it tumbled 

 down from steep rocks into a great lake in which there were 

 divers fruitful isles, store of crocodiles, and {luhichwould be remark- 

 able enotigh if trut) abundance of sea calves, that have no other 

 vent, (Sr-Y., than that by which they take in their food, this lake 

 being in the country of Dambea, three small days' journey from 

 Gundar and four or five days' journey from the source of the Nile, 

 &c., &c." ("The History of the Empire of the Mogul," English 

 translation of 1684, p. 44). 



