274 



NA TURE 



[July 23, 1891 



While townetting during the last few days about the North 

 Cape, we have had some large hauls of Copepoda ; and it 

 occurred to us last night, while watching the midnight sun off 

 the entrance to the Lyngen Fjord, that one gathering might be 

 spared from the preserving bottle and devoted to the i-aucepan. 

 We put out one of the smaller townets (3^ feet long, mouth 

 I foot in diameter) from 11.40 p.m. to midnight, the ship going 

 dead slow, and traversing in all, say, a mile and a half during the 

 20 minutes. The net when hauled in contained about three 

 tablespoonfuls of a large red Copepod {Calamis finmarchicus, 

 I think), apparently a pure gathering — what Haeckel would call 

 a monotonic plankton. We conveyed our material at once to 

 th« galley, washed it in a fine colander, boiled it for a few 

 minutes with butter, salt, and pepper, poured it into a dish, 

 covered it with a tliin layer of melted butter, set it in ice to 

 cool and stiffen, had it this morning for breakfast on thin bread- 

 and-butter, and found it most excellent. The taste is less pro- 

 nounced than that of shrimps, and has more the flavour of 

 lobster. Our 20 minutes' haul of the small net through a mile 

 br two of sea made, when cooked in butter, a dishful which 

 was shared by eight people, and would probably have formed, 

 with biscuit or bread, a nourishing meal for one person. It 

 would apparently, in these seas, be easy to gather very large 

 quantities, which might be preserved in tins or dishes, like 

 potted shrimps. W. A. Herdman. 



S.Y. Argo, Tromso, Norway, July 13. 



Are Seedlings oi Hettierocallis fulva specially Variable? 



I SHALL be grateful to any of your readers who will write and 

 let me know their experiences as to the variability of seedlings of 

 Hemerocallis ptlva, or who will raise it from seed in fair quantity, 

 and kindly communicate to me their results, which shall be duly 

 acknowledged. 



My reason is this : there is in the formation of the pollen in 

 this plant a peculiarity which, according to Weismann's views, 

 should lead to exceptional variability in the seedlings ; but, so 

 far as I know, we have no evidence on the subject. 



Marcus M. Hartog. 



Royal University, Dublin, July 9. 



The Green Sandpiper. 



On Sunday last, July 12, I saw flying round a large pool in 

 Essex, a specimen of the gree7i sandpiper. It flew leisurely 

 round the pool, and seemed as if it were not far from its summer 

 home. I think, therefore, that the bird must be nesting in the 

 county, and probably in the neighbourhood. 



Can any of your correspondents inform me whether the nest 

 has been found anywhere, in recent years, in England ? 



Argyll. 



Argyll Lodge, Kensington, July 17. 



LIQUIDS AND GASES} 



A LMOST exactly twenty years ago, on June 2, 1871, 

 -^*- Dr. Andrews, of Belfast, delivered a lecture to the 

 members of the Royal Institution in this hall, on " The 

 Continuity of the Gaseous and the Liquid States of 

 Matter." He showed in that lecture an experiment 

 which I had best describe in his own words : — 



" Take, for example, a given volume of carbonic acid 

 at 50° C, or at a higher temperature, and expose it to 

 increasing pressure till 150 atmospheres have been 

 reached. In the process, its volume will steadily diminish 

 as the pressure augments ; and no sudden diminution of 

 volume, without the application of external pressure, will 

 occur at any stage of it. When the full pressure has 

 been applied, let the temperature be allowed to fall, until 

 the carbonic acid has reached the ordinary temperature 

 of the atmosphere. During the whole of this operation, 

 no break of continuity has occurred. It begins with a 

 gas, and by a series of gradual changes, presenting no- 

 where any abrupt alteration of volume, or sudden evolution 

 of heat, it ends with a liquid. 



' Lecture delivered by Prof. W. Ramsay, F.R.S., at the R^yJ Institution, 

 on Friday, May 8. 



NO. II 34, VOL. 44] 



" For convenience, the process has been divided into 

 two stages — the compression of the carbonic acid, and 

 its subsequent cooling. But these operations might have 

 been performed simultaneously, if care were taken so to 

 arrange the application of the pressure and the rate of 

 cooling, that the pressure should not be less than 76 

 atmospheres when the carbonic acid had cooled to 31^" 



I am able, through the kindness of Dr. Letts, Dr. 

 Andrews' successor at Belfast, to show you this experi- 

 ment, with the identical piece of apparatus used on the 

 occasion of the lecture twenty years ago. 



I rnust aik you to spend some time to-night in con- 

 sidering this remarkable behaviour ; and, in order to 

 obtain a correct idea of what occurs, it is well to begin 

 with a study of gases, not, as in the case you have just 

 seen, exposed to high pressures, but under pressures not 

 differing greatly from that of the atmosphere, and at 

 temperatures which can be exactly regulated and mea- 

 sured. To many here to-night, such a study is unneces- 

 sary, owing to its familiarity ; but I will ask such of my 

 audience to excuse me, in order that I may tell my story 

 from the beginning. 



Generally speaking, a gas, when compressed, decreases 

 in volume to an amount equal to that by which its pres- 

 sure is raised, provided its temperature be kept constant. 

 This was discovered by Robert Boyle in 1660 ; in 166 1 he 

 presented to the Royal Society a Latin translation of his 

 book, " Touching the Spring of the Air and its Effects." 

 His words are : — 



'"Tis evident, that as common air, when reduced to 

 half its natural extent, obtained a spring about twice as 

 forcible as it had before ; so the air, being thus com- 

 pressed, being further crowded into half this narrow 

 room, obtained a spring as strong again as that it last 

 had, and consequently four times as strong as that of 

 common air." 



To illustrate this, and to show how such relations may be 

 expressed by a curve, I will ask your attention to this model. 

 We have a piston, fitting a long horizontal glass tube. It 

 confines air under the pressure of the atmosphere— that is, 

 some 15 pounds on each square inch of area of the piston. 

 The pressure is supposed to be registered by the height of 

 the liquid in the vertical tube. On increasing the volume 

 of the air, so as to double it, the pressure is decreased to 

 half its original amount. On decreasing the volume ta 

 half its original amount, the pressure is doubled. On 

 again halving, the pressure is again doubled. Thus you 

 see a curve may be traced, in which the relation of volume 

 to pressure is exhibited. Such a curve, it may be remarked 

 incidentally, is termed an hyperbola. 



We can repeat Boyle's experiment by pouring mercury 

 into the open limb of this tube containing a measured 

 amount of air ; on causing the level of the mercury in 

 the open limb to stand 30 inches (that is, the height of 

 the barometer) higher in the open limb than the closed 

 limb, the pressure of the atmosphere is doubled, and the 

 volume is halved. And on trebling the pressure of the 

 atmosphere the volume is reduced to one-third of its 

 original amount ; and, on adding other 30 inches of mer- 

 cury, the volume of the air is now one-quarter of that 

 which it originally occupied. 



It must be remembered that here the temperature is 

 kept constant ; that it is the temperature of the surround- 

 ing atmosphere. 



Let us next examine the behaviour of a gas when its 

 temperature is altered, when it becomes hotter. This tube 

 contains a gas— air — confined at atmospheric pressure by 

 mercury, in a tube surrounded by a jacket or mantle of 

 glass, and the vapour of boiling water can be blown into 

 the space between the mantle and the tube containing the 

 air, so as to heat the tube to 100'', the temperature of the 

 steam. The temperature of the room is 17' C, and the gas 

 occupies 290 divisions of the scale. On blowing in steam, 

 the gas expands, and on again equalizing pressure, it 



