546 



NATURE 



[October 6, 1898 



machine by which he had done it, telling me that he had thought 

 of it twenty years before. I could easily see by the colour of the 

 ink and paper that it must have been done many years. He 

 then told me, what was very certain, that he had neither stolen 

 the thought from me, nor had I from him ; and from that time 

 till his death, Mr. Ellicott was one of my best friends." 



The editor of my copy of Ferguson's works, " David Brew- 

 ster, A.M., 1803," adds that James Ferguson was elected a 

 Fellow of the Royal Society without paying the usual ad- 

 mission fees. This honour he shared with Sir Isaac Newton 

 and Mr. Thomas Simson, the self-taught mathematician. Two 

 Scottish philosophers — David Hume and James Ferguson — died 

 in 1776, both leaving autobiographies of singular beauty and 

 pathos. Our own Huxley, who like James Ferguson was 

 afflicted with "an ineradicable tendency to try to make things 

 clear," has done the same in recent times. Two questions 

 instantly present themselves: (i) On how many distinguished 

 men has this honour been conferred by the Royal Society 

 since these times? and {2), Is there a "watchmaker" now in 

 that learned body ? J. Hughes Hemming. 



Kimbolton, September 24. 



A Case of Inherited Instinct. 



I THINK the interesting cases mentioned by Captain Hutton 

 on p. 411 will hardly bear the interpretation he puts upon them. 

 In New Mexico three genera of Stenopeiinatina: are common, 

 viz., Sienopelinatus, Centhophilus and Udeopsylla. These 

 locusts are nocturnal, and live under logs or in holes in the 

 ground during the day. It is natural, therefore, that they should 

 be attracted by any dark place, such as a cave. The species of 

 Centhophilus, like the crickets, are found in houses, which are 

 well adapted to their tastes. There is no new instinct, or revival 

 of a dormant one, exhibited in this choice. Similarly, in Colorado 

 I have found the species of Centhophilus to live in mines, which 

 are practically caves of recent origin. 



The cave-seeking instinct, therefore, has been practically con- 

 tinuous, and if in New Zealand one genus {Pachyrhavuna) lives 

 in caves, while its ally {Gymnoplectron) is arboreal, it is probable 

 that the former retains the instincts of their common ancestor, 

 while the latter has lost them, so far as the arboreal habit is 

 concerned. T. D. A. Cockerell. 



Mesilla Park, New Mexico, U.S.A., September 15. 



Maggots in Sheep's Horns. 



In a letter which appeared in your issue of September 

 29, Captain Traherne writes under the heading of " Horn- 

 feeding Larvje," of maggots of about half an inch in length 

 and of a white colour, having been found in the horns of 

 a newly killed sheep, which he had obtained in India, but 

 where there were no perceptible signs of perforation. These 

 were not the larvre of a Lepidopterous insect, but of one of the 

 Diptera, known as CEstriis ovis, a well-known parasite. The 

 fly lays her, eggs in the region of the anterior nares, and the 

 larv?e penetrate the nasal passage, finding their way into the 

 turbinal bones, and from thence into the frontal cavity to the 

 base of the horns. Captain Traherne does not say how far up the 

 horn he found them ; they are not usually found beyond the 

 base, but as a rule locate themselves at the back of the throat, 

 where they feed on the mucous substance. They are not horn- 

 feeders. CEstrtis ovis is distributed pretty generally wherever 

 sheep are to be found. 



Mr. Austen, of the British Museum (Nat. Hist.), showed me 

 some very fine specimens, both of the fly and the larvae. 



W. H. McCORQUODALE. 



"Luminous Clouds," or Aurora? 



Surely the " luminous clouds " reported from Cornwall on 

 September 10, in your issue of September 29, were auroral. It 

 is a pity if no other record of altitude has been made, when one 

 observation of such precision is available. I myself have a 

 fairly good record of the upper edge of the bright arch, low 

 down in the N.W. on the previous evening at li p.m., as seen 

 from Croydon. If others have a record of this, a comparison 

 might be of value. 



It may be worth noting the very probable recurrence of 

 aurorje on the evenings beginning with the 6th inst., when the 

 solar revolution produces the conditions of the last magnetic 



NO. I 5 10, VOL. 58] 



outbreak, so far as the aspect of the sun is concerned. I have 



been much struck by this recurrence in working up a series of 



unpublished auroral observations from York, dating back to 1832. 



112 Wool Exchange, E.C., J. Edmund Clark. 



September 30. 



A Hairless Rat. 



I SHOULD like to draw the attention of your readers to a 

 peculiar case which may be worth notice. 



About ten days ago a man employed at the Ordnance Store 

 Department, Stonehouse, brought me what he termed a " real 

 curio." It was a rat, adult though not very old, without any 

 hair on its body. It was caught in an ordinary trap at the 

 Victualling Yard, and it is still alive, active and, to all 

 appearance, healthy. 



in appearance the rat is of a brownish colour, and with 

 the exception of its whiskers, which are normal, and an 

 occasional long woolly hair on the body, it is quite hairless. 

 When at rest the skin is thrown into numerous small folds or 

 corrugations, and its colour is heightened by the dirt which 

 collects in these folds. In active movement the folds disappear. 

 The tail, except an inch at the base, is normal in appearance, 

 though devoid of hair. The ears appear rather larger than 

 usual, and the eyes are somewhat prominent. 



On communicating with the Superintendent of the Zoological 

 Society's Gardens, I was referred to a paper by J. S. Gaskoin, 

 in the Proceedings of the Zoological Society for 1856. A 

 precisely similar case is there described, concerning four mice 

 captured at Taplow in 1854. One of these gave birth to five 

 young, shortly after capture, and these resembled the parent in 

 every respect. There is no plate in the copy of the Proceedings 

 that I have referred to, and the only difference in the description 

 of the mice which does not fit my specimen is the colour of the 

 ears, which are light coloured. T. V. Hodgson. 



Municipal Museum, Plymouth, September 29. 



THE DYNAMICAL THEORY OF REFRAC- 

 TION, DISPERSION AND ANOMALOUS 

 DISPERSION 1 



THE dynamical theory of dispersion, as originally 

 given by Sellmeier,- consisted in finding the 

 velocity of light as afifected by vibratory molecules em- 

 bedded in ether, such as those which had been suggested 

 by Stokes^ to account for the dark lines of the solar 

 spectrum. Sellmeier's mathematical work was founded 

 on the simplest ideal of a molecular vibrator, which may 

 be taken as a single material particle connected by a 

 massless spring or springs with a rigid lining of a small 

 vesicle in ether. He investigated the propagation of 

 distortional waves, and found the following expression 

 (which I give with slightly altered notation) for the square 

 of the refractive index of light passing through ether 

 studded with a very large number of vibratory mole- 

 cules in every volume equal to the cube of the wave- 

 length : — 



+ "'//" 



&c. 



where r denotes the period of the light ; k, k„ k,„ «S:c., the 

 vibratory periods of the embedded molecules on the sup- 

 position of their sheaths held fixed ; and m, m„ m^„ &;c., 

 their masses. He showed that this forrnula agreed with 

 all that was known in 1872 regarding ordinary dispersion, 

 and that it contained what we cannot doubt is substantially 

 the true dynamical explanation of anomalous dispersions, 

 which had been discovered by Fox-Talbot ■* for the ex- 

 traordinary ray in crystals of a chromium salt, by Leroux '•> 

 for iodine vapour, and by Christiansen ^ for liquid solution 



1 Abstract of part of the substance of a communication by Lord Kelvin, 

 G.C.V.O;, to Section A of British Association at Bristol, on September 9. 



2 Sellmeier, Fogg. Ann., vol. 145, 1872, pp. 399, 520; vol. 147, 1872, 

 pp. 386, 525. 



3 See Kirchhoff-Stokes-Thomson, Phil. Mag., March and July i860. 

 •1 Fox-Talbot, Proc. Roy. Soc. Edin., 1870-71. 



5 Leroux, Coinptcs rendus, 55, 1862, pp. 126-128. 



6 Christiansen, Ann. Phys. Ckem., 141, 1870, i p. 479, 480 ; P/iit. Mttt;., 

 41, 1871, p. 244 ; Annates de Chimie, 25, 1872, pp. 213, 214. 



