154 



NATURE 



[October 23, 1919 



radiation, and a consequent reduction in the cooling 

 of the air above it. Local and restricted smudging 

 will not prevent the inflow of colder air from the sur- 

 rounding land where radiation is active. 



In England and on the Continent most of the recent 

 suggestions for frost-fighting have been erroneously 

 based on smoke production ; but in Canada and the 

 United States, although the reason of the inefficiency 

 of smoke production does not seem to have been real- 

 ised, the steps actually adopted for frost-fighting have 

 taken the right direction, aiming at orchard heating — 

 that is, actual heating by artificial means the air and 

 the trees in the plantation. It is true that smudging 

 is still used, but with a very different object, the 

 smudge fires being lighted at dawn to prevent the 

 sun's rays from heating too rapidly the frozen blos- 

 soms, it appears that the damage usually done by 

 frost is not due to the freezing of the contents of the 

 cells and the disruption of the cell-walls, but to the 

 freezing of the intercellular liquid, the formation of 

 ice here resulting in the abstraction of water from the 

 cells ; on thawing, this water is re-absorbed, but only 

 very gradually ; and, if the heating be too rapid, much 

 evaporation occurs before the re-absorption is com- 

 plete, and the cells remain permanently depleted of 

 part of their water. The dehydrating action of freez- 

 ing water in this case is analogous to that observed 

 by the present writer in the case of clay and other 

 highlv hydrated substances, when the liquid in which 

 thev are suspended is frozen. But in those cases no 

 re-absorption of the water occurs on thawing. 



Spencrr Pickering. 



Time Relations in a Dream. 



The following account of a dream which I had 

 last night, and of which I took some notes, may be 

 of interest. The dream commenced by my, as I 

 thought, hearing a drop fall on the laboratory floor ; 

 after a time there was another drop. I then realised 

 that mercury was dropping on the floor from a small 

 split in some rubber tubing in a gas-analysis appara- 

 tus. As I became more wakeful and seemed to realise 

 that I must get up to deal with the leak, the drops 

 fell more rapidly until they were coming quite fast 

 at the moment when I definitely awoke. I then 

 realised that the dropping of mercury which I heard 

 in my dream was in reality the ticking of the clock 

 in my room. 



The point which interested me, and may, I 

 think, interest you, is that of the time relations of 

 the dream. I went over my memory afterwards with 

 a stop watch — and, of course, it is only one's memory 

 of a dream that one ever has to go upon — with the 

 following results : — 



As I dreamed it, the interval between the first two 

 drops seemed to be of the order of five seconds, and 

 the drops seemed to quicken until they were at an 

 estimated rate of about one drop per second. 



Now the actual rate of ticking of the clock was 

 one tick every quarter of a second. It is, of course, 

 evident that one's judgment of time in a dream is 

 quite erroneous in the sense that the occurrences as 

 they take place in the dream seem to extend over a 

 much longer time than the actual time of the dream. 



On the assumption that each consecutive drop in 

 my dream corresponded with one consecutive tick, it 

 would appear that at the commencement of the dream 

 the time interval between two consecutive ticks was 

 exaggerated about twenty-fold in the dream, and that 

 as I got more nearly awake the degree of exaggera- 

 tion became reduced to something like four-fold. At 

 a guess, I heard about thirty drops, in which case 

 the dream would have lasted seven to eight seconds. 



NO. 2608, VOL. IO4I 



There is another possible interpretation, namely, 

 that when I was most soundly asleep only one tick 

 out of twenty came through to my consciousness, and 

 that as I became more wakeful the number increased 

 until one tick in four came through. On the latter 

 theory the dream would have lasted considerably 

 longer than on the former. 



Whatever the interpretation, however, it occurred 

 to me that the time records might be of interest, as a 

 dream is rarely so .simple or of such a kind as to admit 

 of even the vague degree of measurement which I 

 obtained. Joseph Barcroft. 



Physiological Laboratory, Cambridge, October 14. 



International Relations in Science. 



A ciRCUL.'iR letter has been addressed, within these 

 last few days, to " Members of the Academies of the 

 Allied Nations and of the United States " by their 

 brethren of the learned societies of the neutral 

 countries. It is an appeal for toleration, even for 

 generosity, an earnest and eloquent protest against a 

 policy which would seek to exclude the present genera- 

 tion of Grerman scholars and men of science from all 

 our scientific and scholarly intercourse. 



I cannot say that I have always been on the side 

 of tolerance and reconciliation ; but already we have 

 had some little time to think, and this all but cosmo- 

 politan appeal is bound, as it seems to me, to become 

 a factor in the case. It is signed by very many friendly 

 and honoured names ; we cannot shut our ears to it, 

 we cannot resolve upon isolation, lest it be isolation 

 indeed. 



This is not a matter to be decided for us by the 

 votes of others, but by each man for himself — b\- all 

 who claim liberty of action and freedom of thought. 

 I am convinced that very many men feel, as I feel, 

 that whatsoever overtures our German. speaking col- 

 leagues may make to us on matters scientific should 

 be freely reciprocated. Need we ask what a man has 

 thought or said, or even what he has done, in (hese 

 last sad years? If he come in the universal name of 

 science let that suffice ; let it be granted that he m(^ans, 

 now and henceforth, to follow the paths of learning 

 and to walk in the way of peace. 



St. Andrews. D'Arcy W. Thompson. 



INTERNATIONAL ORGANISATION IN 

 SCIENCE. 



A N appeal addressed "to the members of the 

 ■^*- Academies of the Allied Nations and of the 

 United States of America " and signed by a 

 number of scientific and literary men in neutral 

 countries has been circulated and has already 

 given rise to comments in the Press. It deals 

 mainly with the formation, by the Allied 

 academies, of new international scientific associa- 

 tions which neutral countries are now invited to 

 join. Stripped of its rhetorical clothing, the docu- 

 ment is an appeal to let bygones be bygones and 

 to allow science to become again "the great con- 

 ciliator and benefactor of mankind." 



There will be much sympathy with the argu- 

 ments used, the regrets expressed, and the hopes 

 foreshadowed by our neutral friends, but they 

 have left untouched, and to a great extent mis- 

 understood, the principal considerations which 

 have driven the allied academies to the policy 

 they have adopted. It is only that part of our 



