388 



NATURE 



'Feb. 



iSSi 



almost a sealed book to us. By a little attention we might hear 

 of still more carious things in this field. Phone 



New York, November 20, 1S80 



Subsidence of Land caused by Natural Brine-Springs 

 A THEORY has been put forward to account for the subsidence 

 of land in the salt districts of Cheshire. It is said that, sup- 

 posing the manufacturers of salt ceased to pump up the brine, 

 it would run away to the sea, and subsidence would go on at as 

 rapid a rate as now. Can any of the readers of Natijiie tell 

 me of any facts to substantiate such a theory, or refer me t j any 

 district where such rapid subsidence is going on, owing to tlie 

 escape of natural brine-springs to the sea? Any reference to 

 works giving information on this point will be thankfully 

 received. Thos. AVard 



Northwich, February 15 



Chlorophyll 



The following experiment may be interesting in its bearin;^ on 

 the relation between chlorophyll-development and li;^ht. 



If cress seed are grown for a few days in the dark on damp 

 cotton- wool, and then, beneath the surface of water, introduced 

 into an inverted glass jar filled with water, they may be expo>ed 

 to daylight for an indefinite time without chlorophyll bein:j 

 developed. But the plants are not dead ; for if, after a few 

 days' exposure, the cjtton-wool on which they have been grown 

 is cut in two beneath the surface of the water, and one half, 

 with its plants, is restored to the inverted jar of water, while the 

 other is placed under an inverted glass jar containing air only, 

 and then these two jars be exposed to full daylight, the plants 

 beneath the jar containing air rapidly become green, while the 

 others never do so. 



Light therefore cannot always cause the development of 

 chlorophyll in the etiolated leaves of living plan's. 



Liverpool, January 24 William Carter 



[This is an interesting observation, but seems to need some 

 further investigation. As shown by Sachs ("Text-book," pp. 

 565, 656) the formation of chlorophyll has a complicated depen- 

 dence upon light. II the temperature be sufficiently high it i; 

 formed in the cotyledons of conifers and the leaves of fern^ even 

 in complete darkness. The seedlings of angiosperms require 

 exposure to light for the production of chlorophyll, but it due< 

 not take place at low temperatures. All the visible parts of the 

 spectrum possess the power of turning etiolated grains of chloro- 

 phyll green, although the yellow and adj jining rays are most 

 effective. The failure of the .'seedlings immersed in water to 

 become green can hardly therefore be attribute 1 to the absorp- 

 tion of the heat rays. Is it possible that their water-bath keejis 

 their temperature too low?] 



Squirrels Crossing Water 



In Nature, vol. xxiii. p. 340, I read that Mr. Godwin- 

 Austen never had heard of a squirrel taking to the water. As 

 here are perhaps more readers of Nature in Mr. Godwin- 

 Auhten's case, I take thi; opportunity to transcribe what 

 Bachman related to us about that matter in the year 1839. 



The northern grey and IJack squirrel Sciurus leucotis, has 

 occasionally excited the v. onder of the populace by its wandering 

 habits and its singular and long migrations. Like the lemming, 

 LeviHus iiorvegicus, of the Eastern Continent, it is stimulated, 

 either from a scarcity of food or from some other inexplicable 

 instinct, to leave its native haunts and seek for adventures or for 

 food in some distant and, to him, unexplored portion of our 

 land. The newspapers from the West contain frequent details 

 of these migrations ; they appear to have been more frequent 

 in former years than at the present time. The farmers in the 

 Western wilds regard them with sensations which may be com- 

 pared to the anxious apprehensions of the Eastern nations of 

 the flight of the devoiu-ing locust. At such period.s, which 

 usually occur in autumn, the squirrels congregate in diflcrent 

 districts of the far North- West, and in irregular troops bend 

 their way instinctively in an eastern direction. Mount uns and 

 cleared fields, the head-w aters of lakes and broad rivers, present 

 no unconquerable impediments. Onward they come, devouring 

 on their way everything that is suited to a squirrel's taste, laying 

 waste the corn and wheat-fields of the farmer ; and as their 

 numbers are thinned by the gun, the dog, and the club, others 

 are ready to fall in the rear and fill up the ranks, till they occa- 

 sion infinite mischief and call forth no empty threats of revenge. 



It is often inquired how these little creatures, that on common 

 occasions have such an instinctive dread of water, are enabled 

 to cross broad and rapid rivers, like the Ohio and Hudson, for 

 instance. It is usually asserted, and believed by many, that they 

 cany to the shore a suitable piece of bark, and seizing the 

 opportunity of a favourable breeze, seat themselves upon this 

 substitute for a boat, hoi,t their broad tails as a sail, and float 

 safely to the opposite shore. This, together with many other 

 traits of intelligence ascribed to this species, I suspect to be 

 apocryphal. 1 hat they do migrate at irregular and occasionally 

 at distant periods is a fact sufficiently established ; but in the only 

 instance in which I had an opportunity of witnessing the migra- 

 tions of the squirrel, it appeared tome that he was not only an 

 unskilful sailor, but a clumsy swimmer. It was (as far as my 

 recollection serves me of th; period of early life) in the autumn 

 of 180S or 1809, troops of squirrels suddeiilv and unexpectedly 

 made their appearance in the neighbiurhood, but among the 

 grey ones were varieties not previously seen in those jjarts ; some 

 were broadly striped, with yellow on the sides, and a few with 

 a black stripe on each side, bordered with yellow or brown, 

 resembling the stripes of the little chipping squiiTel ( 7a/«;Vrj 

 lysteri). They swam the Hudson in various places between 

 Waterford and Saratoga ; those which I observed crossing the 

 river were swimming deep and awkwardly, their bodies and 

 tails vholly subaierged ; several that had been drowned were 

 carried downward by the stream, and those which were so for- 

 tunate as to reach the opposite bank were so wet and fatigued 

 that the boys stationed there with clubs found no difficulty in 

 securing them alive or in killing them. Their migrations on 

 that occasion did not, as far as I could learn, extend farther 

 eastwardly than the mountains of Vermont ; many remained in 

 the county of Rensellaer, and it was remarked that for several 

 years afterwards the squirrels were far more numerous than 

 before. It is doubtful whether any ever return westwardly ; 

 but finding forests and food suited to their tastes and habits, 

 they take up their permanent residence in their newly-explored 

 country ; there they remain and propagate their species until 

 they are gradually thinned off by the effects of improvement 

 and the dexterity of the sportsmen around them. (The Maga- 

 due of Natural History, vol. iii., new series, 1839.) 



Leyden, February 16 F. A. Jentink 



Flying-Fish 



With reference to the letter of Mr. Pascoe in Nature, vol. 

 xxiii. p. 312, allow me to offer a suggestion as to the mechanical 

 means by which the flying-fish moves when out of the water. 

 During a voyage to India and back I took a great interest in 

 observing the movements of the-e beautiful creatures by means 

 of a powerful opera-glass; and soon came to the conclusion that 

 a slight but rapid tremor of the pectoral fins could. be seen for a 

 few moments after the fidi left the water. In very calm weather 

 I noticed a series of little ripples on each side of the fish as it 

 skimmed along the surface before ri.sing for its flight, evidently 

 caused by the uing-points tipping the water. My idea is that 

 the flying-fish springs from the sea, and by beating the surface 

 rapidly with its pectoral fins obtains an impetus v\hich carries it 

 along for some distance in the air. It then descends to the 

 surface, and in the same manner acquires a fre~h accession of 

 speed. This process however is never repeated more than twice, 

 though the fish does sometimes resume its flight after a moment 

 of immersion. R. E. Taylor 



THE TRANSIT OF VENUS 



THE President of the Royal Society presents his com- 

 pliments to the Editor of N.\ture, and will be 

 much obliged to him if he will, at as early a date as 

 may be convenient, be so good as to give publicity to the 

 enclosed minute of the Transit of Venus Committee. 



The Royal Society, Burlington House, 

 London, W., February 21 



" The Committee appointed by the> Royal Society, at the 

 request of the Government, to make arrangements for 

 observing the Transit of X'enus in 18S2, would be glad to 

 be informed whether astronomers have at their disposal, 

 and are willing to lend, for use in the observations, 4-inch, 

 5-inch, or 6-inch refracting telescopes, and lo-mch or 

 12-inch reflectors, with equatorial mountings ; also port- 

 able transits or altazimuths. 



