ytiiie 24, 18S0J 



NA TURE 



171 



line and returning to our starting point, the perpendiculars will be 

 found pointing in a direction the opposite of that with which we 

 started." Here then is the solution of the difficulty. As we 

 move over our surface along a geodesic, the instantaneous 

 Euclidian plane containing the beginnings of successive perpen- 

 diculars (for small inilial portions of two successive perpendicu- 

 lai's to a geodesic will lie in a Euclidian plane) rotates about the 

 instantaneous tangent to the geodesic, and it does not complete 

 a rotation until we have travelled t-ai:e the complete length of 

 the geodesic. The perpendicular is a vector quantity, and 



changes sign by passing through - V^- Also, a geodesic does 



2 

 not divide the surface into two completely separate regions, as a 

 great circle does a sphere or a straight line a plane. The two 

 regions are continuous with one another, and it is possible to get 

 from the one to the other along a finite path without crossing the 

 geodesic. F. W. FranIsLAND 



Registrar-General's Office, Wellington, 

 New Zealand, April 14 



Ascent of Etna 

 It was a bright sunny sky on the last day of April when we 

 started, with Giuseppe Sedici as guide, from the Grand Hotel at 

 Catania in a carriage and pair bound for Nicoloni, en route to 

 the summit of Etna. A dusty drive of two and a half hours, 

 and we were at the door of the inn in the centre of the village. 

 Its appearance was somewhat forlorn, and its fare rather meagre, 

 but the civility of mine host compensated for all other defects. 

 Here we engaged two mules, a porter, and a driver, an operation 

 which took more than two hours, and then set off again for the 

 Casa del Bosco, which we reached in the middle of the afternoon 

 after a ride of two and a quarter hours. A climb up a neigh- 

 bouring hillock to see the sunset, dinner,*and a few hours' rest 

 filled up the time till II p.m., when we started off again |and 

 rode for about half an hour, till the appearance of snow made it 

 necessary to dismount and continue the remainder of the journey 

 on foot. Our guide was very slow, and on any attempt to force 

 the pace stood still and ejaculated: " Fermo, Signore! Piano, 

 Piano ! " so that we did not arrive at the Casa Inglese till 

 5 a.m., and were obliged to content ourselves with seeing the 

 sun rise from here instead of from the top, as we had intended. 

 It did not much matter, as it was a cloudy morning, and the 

 view was very poor, but still it was a disappointment. The 

 Casa Inglese was covered with snow to the eaves of the roof, the 

 observatory buried altogether, the Val del Booe a sea of white. 

 After a short rest we trudged on again ; so far it had been good 

 walking up an easy ascent of crisp snow, but now it became a 

 work of difficulty to pick one's way through deep drifts and 

 treacherous-looking holes, which seemed to explain the guide's 

 reluctance to undertake this part of the route by moonlight. 

 Arrived however at the foot of ihe c^ne, the snow ceased, and a 

 heavy climb up the frozen side under a biting wind began. Half 

 way up matters were not improved by a severe attack of siclines ; 

 but at length the top was reached at 6.20 a.m. There was no 

 dist.ant view ; within the crater the steam and smoke kept being 

 l)lown hither and thither, and cleared off at times sufficiently to 

 show parts of what looked like a bottomless pit. It was a 

 curious and weird sight altogether, and well repaid the fatigues 

 of the journey. During the descent the notes of the cuckoo and 

 some very sweet violets found by chance under the snow reminded 

 us that, notwithstanding the mountain's wintry mantle, of white, 

 it was really spring time, and that the morning sun had ushered 

 in the merry month of May, a fact which we had well nigh 

 forgotten but a few hours before, when our fingers were numb 

 with cold and our ears threatened to become a thing of the past. 



G. 



Colour Combinations 



The production of white by red and green solutions is well 

 seen on mixing cobalt and nickel solutions together in proper 

 proportions. Another interesting example is that of electrically 

 deposited copper immersed in a solution of copper sulphate. 

 The first notice of this, so far as I know, occurs in Shaw's 

 " Manual of Electro-Metallurgy" (1842), p. 33, in the following 

 terms ; — 



" This phenomenon may be observed in great perfection by the 

 electrotype ; the solution of sulph.ate of copper is of an intense 

 and pure blue ; and the newly-precipitated ductile copper is of 



an equally pure orange ; let the reader take a vessel containing 

 the cupreous solution and place it in the sun, in order to have an 

 abundance of light, and immerse in it, in a horizontal position, 

 a piece of new electrotype copper ; immediately the metal sinks 

 beneath the surface of the blue solution the orange tint fades, 

 and by placing it at a proper depth altogether vanishes, and the 

 metallic plate ai>pears inten'ely white ; when nicely adjusted the 

 plate so much resembles pla-ter-of-paris that a person unac- 

 quainted with the nature of the experiment would with difliculty 

 be persuaded that it was not made of that substance." 



Birmingham and Midland Institute, C. J. Woodward 



June 14 



P.S. — In mixing red and green solutions is it correct to speak 

 of them as proJucingvihiit'! I take it that the mixture absorbs 

 more light than the two solutions would do if separate, i.e., the 

 solution of nickel transmits a greenish white, the cobalt solution 

 a reddish white, but together the red and green destroy each 

 other, the excess of white light passing through. This is shown 

 forcibly by using strong solution^-, when tl;ie deep red and green 

 produce, not white, but black.— C. J. W. 



Wild Swans — Notes of Birds 



There are at present eight wild swans in a lake not far from 

 here. I believe them to be part of a flock of sixty which were 

 there all through the w inter. Wild sw ans in summer were never, 

 so far as I know, heard of in this part of the world before. I 

 have always carefully preserved the wild fowl on this lake, and 

 I pay increased attention to the swans, which I hope will be safe 

 from poachers. They swim in pairs, but show no signs of 

 nesting. 



The major cuckoo noticed in my letter (NATURE, vol. xxii. 

 p. 76) is still here without any other major that I could find in 

 this place or in the neighbourhood. Referring to your polite 

 correspondent A. N., in p. 97, I must 'emark, for the fair fame of 

 the cuckoos, that his theory relating to sex seems quite unsustain- 

 able. Certainly if all the minor cuckoos about here were males 

 and the single major a female it would show an instance of 

 polyandry (if the term can be applied to birds) such as could 

 scarcely be matched in the whole range of natural hi-tory. I 

 quite agree with Mr. New-ton (p. 122) that the female cuckoo 

 does not sing; and it might peihaps be unamiably suggested 

 that the comparative silence of the females among the lower 

 animals .seems among the most marked distinctions between them 

 and the human race. 



Regarding Mr. Allen's letter (same page) I can only say that, 

 while his experiences are so different from mine, there must be 

 an imperfection of ear in either of us, and, without any notion of 

 insisting on the correctness of my own, I should like, at least, to 

 hear the testimony of other parties in the matter. Of course I 

 referred to cuckoos in full voice in the height of the season. 

 When their voice begins to decline, their notes vary, and, as a 

 friend of mine expresses it, they " sing anyhow." 



Millbrook, Tuair, June iS J. Birmingham 



Anchor-Ice 



Allow me to say in re|)ly to Mr. Rae's kindly criticism 

 (Nature, vol. xxii. p. 54) that I did not assert that the original 

 ice-co'stals are "at least as heavy as water," but that they 

 " seem" to be so (vol. xxii. p. Si). 



I have seen them collect upon stones at the bottom of wafer- 

 ways two or three feet in dcith — where the stream though swift 

 was smooth and unbroken, — and I have thought that this might 

 be the result of their having a greater specific gravity than 

 ordinary ice. 



In my desire to be concise I had ihe misfortune to use a phrase 

 that gave Mr. Rae the impression that I was asserting as a fact 

 that which at best I have only regarded as possible. 



Boston, June 7 C. F. C. 



SCIENTIFIC RESULTS OF THE HOWGATE 

 POLAR EXPEDITION, 1877-7S 



THE fifteenth Bulletin of the United States National 

 Museum (Washington, 1879) consists of contribu- 

 tions to the Natural History of Arctic America, made in 

 connection with the Howgate expedition in 1877-78, by 

 Ludwig Kumlien, naturalist to the expedition, who gives 



