Dec. 29, 1882. 



- KNOWI.EDGE 



499 



Try 



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BRITISH SNAKES. 



[668] — The three British snakes are the Viper, Einged Snake, and 

 the Smooth Snake, (coronella loevis). The Smooth Snake is as 

 local in England as on the Continent — indeed, I do not recollect any 

 records of its occurrence hitherto, except in Hants and Dorset. 



It becomes tame in confinement, and though it may sometimes 

 try to use its teeth, it belongs to a perfectly harmless genus. The 

 plate in Cook's "Reptiles" conveys a fair idea of the Smooth Snake, 

 but living examples can often be examined at the Reptile House of 

 the Zoological Society, on application to the keeper. The Smooth 

 Snake subsists mainly on lizards. H. A. JI. 



COLD BATH AT XIGHT. 



[669]— In reference to A. E. Oram's query (605, page 36-t) as to 

 the healthfulness of a cold bath at night, I should be inclined to say 

 that— as a practice — it is not healthy. After a hard day's work, 

 when the muscles are wearied or the nerves strained, a warm bath 

 is undoubtedly very comforting, and is also in a sense beneficial, as 

 it produces a relaxation of the stiffened muscles. A cold bath, on 

 the other hand, has an astringent effect, and must necessarily cause 

 further contraction of the muscles. (In plethoric persons there 

 would also be a risk of congestion of the lungs or brain.) For my 

 o^vn part, I decidedly object to the idea of a cold bath at night after 

 a hard day's work. naj.i.- 



This opinion is, of course, one on the general question merely. 

 Robert Macpbersox, M.D. 



SINGULAR RAINBOW. 

 [670] — In letter 637, Knowledge, Nov. 24, the writer evidently 

 does not grasp the whole problem. In a communication sent to 

 the Physical Society, London, Nov. 10, and read Nov. 25 (a copy of 

 which I have forwarded to you), I have shown (1) that for the 

 observer to see a complete non-concentric bow he must be sur- 

 rounded by water, and also what parts of the bow he sees if the 

 rellecting sheet of water be only behind, before, or to one side of 

 him ; (2) that the non-concentric bow is inclined to the reflecting 

 plane at an angle equal to the angle of incidence of the light falling 

 on this same plane ; (3) that the non-concentric bow has been seen 

 only when the sun has been at a low altitude, on account of there 

 being at such times a maximum of light reflected and a minimum 

 ot loss from polarisation ; and (i) that at such an angle as that 

 given in the second figure (letter 637), Knowledge, p. 422, it would 

 be impossible to see a complete non-concentric bow on account of 

 polarisation. William Ackroyd. 



HOVERING INSECT HOUSE-FLIES. 

 [671] — No one has answered Mr. Wynne's note, Xo. 016, so the 

 following information may be useful : — 1 never heard of such 

 an insect as an ichneumon wasp ; they (the ichneumons and 

 the wasps) are two distinct families of the order Hymonoptera, 

 and do not hover as ho describes. The insect ho has observed is 

 without doubt a dipterous fly of tho family " Syrphida>," either 



" Eristalis " or " Syrphns," probably the common " Eristalis tenai." 

 Tliey are often called " hovercrs " from their peculiar flight. .\s 

 regards the number of vibrations of the wings, I can give him i.'- 

 information, but I^tour has calculated those of a common gnat ;r 

 3,000 a minute (Kirby & Spence, p. 59). 



In answer te M. D. (No. 033), I am afraid he is very much mis- 

 taken in stating that bluebottles are developed within the body of 

 the female fly in a maggot state. All flies are produced from eggs 

 laid in or on the substance upon which the maggots afterwards feed, 

 and they breed so rapidly that a very few specimens of hybemateil 

 impregnated females who lay their eggs in the spring will produce 

 the numbers he sees every year. The same holds good with a 

 number of otier insects, notably wasps and bumble-bees, who may 

 be seen on the move, and looking out for a suitable place for their 

 nests on a fine spring morning. Destroying them at that tiii' 

 means destroying a whole nest ; and if then hunted and killed, wi: 

 make a distinct diminution in the number of nests in the immediai> 

 neighbourhood. 



Reaumur has proved that in five generations an aphis can be tl.' 

 progenitor of 5,904,900,000 descendants, and that there can 1 • 

 twenty generations in one year (Kirby, p. 96). The flies dont f. 

 on quite at this rate, but they are what the Yankees call "pretty 

 smart." As to their disappearance in the autumn, I think tl.' 

 spiders and the frosts quite account for that. 



An Old M. E. S. 



ISLANDS IN PACIFIC OCEAN AND EATS. 



[672] — My experience has been quite opposed to the state- 

 ment made in Knowledge of 17th ult. on the above subject. 



I lived for about a year on the largest island of a small grou;. 

 called Labos de Afuera (important chiefly on account of the deposit - 

 of guano on them), situated in about 7° south latitude, and fifty • : 

 sixty miles from the Peruvian coast. 



I occupied a portion of a large modem house, which, I might s.n 

 was infested with rats. I have been repeatedly wakened at nijr! 

 by the rasping noise they made in their endeavours to force thiv 

 wav into mv bedroom. Sometimes two would be simultaneously :i * 

 work — one near the bottom of the wall, or partition, the other nen : 

 the ceiling. Where an entrance was effected, I used to get np, an' 

 arming myself with a stick, give the intruders chase. 



They were a great nuisance, and I would have been heartily gl.i i 

 if they had all been carried off by a rapid consumption. Twocat- 

 which we had (first-rate ratters) nsed to reduce their numbers con- 

 siderably, but they still continued to increase. On one occasion I 

 found a nest under a water-butt, containing, if I remember rightly, 

 ten little rats. 



Nothing in the shape of eatables was safe from these vermin : 

 they even attacked onr live-stock, such as pigeons and chickens. 

 J. H. M. Fallon. 



ALTERATION IN CDAST LINE. 



[673]— I thought it very interesting to observe how the sea hr 

 receded along the coast of Lancashire from the Mersey almost t 

 Preston. The whole country for miles is as flat as the provcrbi: 

 pancake, and it can at once be seen that all this land, wliich is ei 

 tirely made up of sand, must have been gradually formed by tl 

 retrocession of tho sea. 



At Sonthport, at low tide, the water goes out for at least t\v 

 miles, the head of the pier, which is nearly a mile long, being ju 

 kept free of sand by a channel which runs by it. The tide seems i 

 ebb almost at once for a considerable distance ont, and the tin 

 cannot be very remote when Sonthport will be an inland town. 



Are there any data showing the rate the water is receding nioi 

 tho Lancashire coast ? H'sktt. 



Oct. 17, 1882. 



ansftwrifii to CorifsponiJfnts. 



Reapers, tilnd to find vou among renders, whether you hail from 

 Giggleswick, Cambri.lge,' Rugby, or Clifton. I foar you have 

 given some lime to logic. No offence : so have I ; and 1 wish tho 

 time had been bettor besto^ved. But the four you name were 

 teachers, not students only. Besides, their reasoning powers would 

 have stood a pood deal of impairing. Vet can you name any useful 

 product of their logic ? Note, further, that it was ono of tboso 

 \ery four who said that certain false reasoning would misload 

 students of logic, though its falsity is obvious to persons of onlinary 

 reasoning iwwors. You write rather snappishly. Perhaps it 

 misled you. Well, well I But you should not be angry with m. . 



