158 



KNOWLEDGE. 



[July 1, 1899. 



made by him, over a period of four years, on the tempera- 

 ture inside tree trunks. When the trunks and limbs of 

 trees are shaded, their temperatures, if above that at which 

 water freezes, vary according to the temperature of the 

 outside air. Moreover, in the shade, tree temperatures 

 above the freezing point of water are higher than the air 

 temperature when both are falling and lower when both 

 are rising. When exposed to bright sunlight, however, 

 the tree temperatures, in circumstances otherwise similar, 

 are higher than the air temperature, not only when both 

 temperatures are falling, but are often higher also when 

 both are rising. One side of even a small limb may 

 consequently have a temperature much higher than the air 

 and the opposite side a temperature lower than the air. 



A recent meeting of the Linnean Society was very full 

 of interest. Mr. Botting Hemsley, f.b.s., exhibited plants 

 from high altitudes, collected by several well-known ex- 

 plorers. Mr. Valentin sent photographs and lantern 

 slides of an elephant seal eighteen feet in length, which he 

 recently examined alive on the shore on the Falkland 

 Islands. It was a male, the trunk being only possessed by 

 this sex. The latter was inflated till it was a foot in length 

 from the tip to the gape. Mr. Harting had living specimens 

 of the rarer British vole from Skomer Island, off the coast 

 of Pembroke. The young are brown, the adults reddish, 

 and the hair grows remarkably fast. The President, 

 Dr. Giinther, produced a letter bearing upon the case of 

 the gigantic land tortoises of the Seychelles, sent by the 

 Administrator there to Mr. Chamberlain, and exhibited 

 photographs of several specimens. The letter arose out of 

 Dr. Giinther's presidential address of last year, which 

 treated of these reptiles and their chances of soon becoming 

 extinct. Afterwards Sir John Lubbock read a paper on some 

 wingless insects of Australia, and, finally, an account was 

 given of a unique specimen of a crustacean found in a whale. 



It is now over twenty years since Raoul Pictet, of Geneva, 

 announced the results of experiments carried on with the 

 object of liquefying that most refractory of all the so-called 

 permanent gaaea—hyflrogen, but up to a week or two ago 

 all efforts in this direction were, at the best, problematical 

 and unconvincing. Now, however, a grand achievement 

 has been effected by Prof. Dewar and his able assistant, 

 Mr. Robert Lennox. These investigators, by the undoubted 

 liquefaction of hydrogen, have put the finishing stroke on 

 the line of research initiated by Faraday when he first 

 reduced the gas chlorine to a liquid. The new agent of 

 scientific research — liquid hydrogen — congeals the air 

 surrounding the containing tube into a snow-like solid, 

 and a piece of cork sinks to the bottom when put in the 

 liquid; the temperature at the boiling point is 21" absolute, 

 or - 252°, a temperature representing a pressure which is 

 immeasurable. The liquefaction of hydrogen is a triumph 

 of theory as well as practice, for in face of all the enormous 

 difficulties which have been encountered, theorists have 

 never deviated one jot from the conviction, which sound 

 reasoning long ago showed, that there is no such thing as 

 a permanent gas. 



^vitisf} (3rmfi}o\oq\tn\ Notes. 



Conducted by Hasry F. Witherbt, f.z.s., u.b.o.u. 



" Nightingale Thrushes." — Between Eltham and Sid- 

 cup, Kent, are several thickets in which the Thrush 

 abounds, and in which the Nightingale is very common in 

 its season. The effect of this close association of the 



species is apparent in the song of some of the Thrushes 

 there. In January and February a wonderfully good 

 rendering of some typical strain of the Nightingale is often 

 heard from a Thrush. A friend remarked upon this, he 

 having felt assured that he was listening to a Nightingale 

 (in March) until the bird was revealed close at hand as a 

 Thrush. The Thrushes never attain to a good rendering 

 of the long-drawn sweet note of the Nightingale, but they 

 try to do it, and give a long " straight " whistle, like 

 " pee pee pee," in the effort. Some of the other strains, 

 however, are more successful. I have heard the 

 " pee pee pee boblobloble " and the full bubbling note 

 (like that of the Lesser Whitethroat) given with exactly the 

 emphasis and accent of a Nightingale, by a February Thrush. 

 Then the alarm, " whit-urrrr," of the Warbler has been given 

 with exactness two months before the arrival of the bird. 

 Many of the phrases of the Thrushes at the spot indicated 

 also include a very rapid repetition of two notes many 

 times, one note being a few tones higher than the other. 

 This is a feature no doubt derived from the Nightingale, 

 whose song so often contains a similar variation. Near 

 Charlton Kings, in Gloucestershire, late in March, I heard 

 a Thrush give a true strain of the Nightingale, and asked 

 if the latter bird had not been found there last year. 

 The answer was that a Nightingale had been heard close 

 to the spot. My observations lead me to conclude that 

 the best singers of Thrushes and Robins (at least) are 

 found not rarely year after year in the same spots. I 

 never heard the Eltham Blackbirds try to imitate the 

 Nightingale, but one of them, this year, was certainly 

 uttering a song consisting sometimes of nothing but one 

 note repeated, and that note was also the note of some 

 young Ducks ! The Ducks had been there for a couple of 

 months or more, and were noisy as usual— with the result 

 that the poor Blackbird found himself unable to originate 

 any better song than a kind of musical " work work 

 work." He would give five or six phrases of nothing but 

 this note, then add a few whistled sounds. This incident 

 was chiefly noticeable at dawn ; and it was plain that the 

 Blackbird was very desirous to utter a nobler song, for 

 after a time he wholly abandoned the primitive strain, and 

 sang only the usual, varied, full songs of his species. — 

 Charles A. Witchell, 



Spring Immigration of the Golden-crested Wren. — 

 There was a very considerable immigration of Golden- 

 crested Wrens on the Yorkshire coast in the third week 

 of April. At Flamborough on the 21st they swarmed, and 

 in the Spurn district were numerous on the 18th and 

 subsequently, some being picked up dead, which fact is 

 suggestive of a long and exhaustive flight. The wind 

 during the period was strong north-east, and the weather 

 was hazy. This movement of the Golden-crested Wrens is 

 very remarkable, as, so far, we have no notice or record 

 of a spring immigration of the species. We know that 

 immense numbers arrive in October on our eastern shores 

 at the same time as the Woodcocks, and that many again 

 leave the country about the last week of March or early 

 April at the same time when the Woodcocks are leaving. 

 The spring movement is, however, much less observable, 

 as these small wanderers then approach the coast in strag- 

 gling fashion and not in the larger flights of autumn. 

 Under unfavourable meteorological conditions I have 

 known them congregate in considerable numbers in the 

 coast hedgerows, biding their time. This spring immigra- 

 tion of Gold-crests has, probably, been caused by migratory 

 flocks going north meeting with bad weather over the 

 North Sea, driving them considerably westward of their 

 normal route on to the East Coast of England. — John 

 GoRDEAux, Great Cotes House, R.S.O., Lincoln. 



