NA 7 URE 



[April 22, 1909 



the chilling- of the water, and this, of course, pre- 

 supposes that the pond is fairly full, otherwise there 

 would be no water-surface at all to speak of. Perhaps 

 it is intended that when empty the puddled clay 

 commences the operation, and when the water has 

 arrived this carries on the process. What evidence 

 is there that this is so? The chief evidence is found 

 in that ice is obtained in India by placing pans of 

 water in shallow beds filled with rice-straw. 



This is excellent so far as it goes, and Dr. Wells 

 records that he performed the same experiment in 

 England nearly a hundred years ago. Thus there is 

 a presumption that if straw be laid down under a 

 pond, it may act in such a way as to cut off the 

 heat of the earth below. The difficulty lies in carry- 

 ing out a similar process on a large scale, and at 

 the same time in keeping the straw dry. Should it 

 become moist, and it must do so if in contact with 

 puddled clay, it will cease to be an efficient non-con- 

 ductor of heat, and it must be borne in mind that 

 whereas the straw under the ice-pans in India can be, 

 and is, frequently changed, this cannot be done under 

 a pond. Mr. Hubbard says : — " In numerous dew- 

 ponds in this country the dew-point is reached without 

 difficulty." Nothing is given in support of this state- 

 ment, and we may well ask on what evidence it is 

 based. It presumably means that the water itself 

 reaches a temperature which is below the dew-point. 

 A number of observations made by the writer have 

 never yet revealed the fact. The water of a 

 pond parts with its heat extremely slowly. To be 

 of value toward the replenishment of a pond, the 

 dew must be received in the height of summer, when 

 there is but little rainfall, and when, as is admitted, 

 the ponds at lower levels are drying up. The pond 

 is heated during the day, and evidence is wanting 

 as yet that it falls below dew-point at night. Of 

 course, dew is being received on the grassy banks 

 around, that is to say, on vegetation, but the radiat- 

 ing powers of water and grass are apart as the poles, 

 and on radiation dew-fall, as we know it, depends. 



As Mr. Hubbard states, the altitude of the ponds 

 may result in some amount of condensation, owing 

 to the lowering of temperature resulting from the 

 expansion of the air. This would, however, be but a 

 small factor, whilst the condensation would show 

 itself as mist. There mav be something, too, but not 

 much, in the osmotic action of dew-pond water, con- 

 taining as it does a small proportion of sodium 

 chloride. But there must be some greater factor at 

 work if we are to credit the few records which have 

 been made of the acquisition of, for instance, " 35 

 inches of water after five nights of heavy dew." 



Mr. Hubbard rightly judges the importance of 

 the dew-pond principle, if fully established, in coun- 

 tries where there is no natural water-supply other 

 than dew. He is also quite correct in dwelling upon 

 the importance of vegetation in increasing the rainfall 

 of a district. But when we hear of the rising of the 

 water in a pond by an inch or more in a night, we 

 desire to know if there are any overhanging trees, 

 and whether there are grasses rooted in the bottom 

 of the pond, with several inches of their growth ex- 

 posed to the atmosphere. The dew deposited on these 

 would be a large item, and would go to feed the 

 pond. Still, there are undoubtedly some ponds, of 

 large size, with no vegetation appearing above the sur- 

 face, no drainage except from their own shelving bank, 

 the only visible means of recruiting of which consists of 

 rain and driving mists. Given a period of drought, 

 yet these ponds seem to suffer but little. I am not at 

 all satisfied that straw is really a necessity of the case. 

 I have collected information from several different 

 quarters as to the manner of construction of dew- 



NO. 2060, VOL. 80] 



ponds, but straw is not used in all cases, and when 

 used it is frequently placed above the clay merely 

 to prevent cattle from trampling through the bottom 

 and so allowing the water to escape. If dew-point 

 is reached in the air above a pond, there must be 

 some other factor than the alleged chilling of the 

 clay or the w^Tter to bring it about. There is room 

 for more experiment. E. A. M. 



At the last meeting of the Royal Society the following- 

 were elected foreign members of the society : — Prof. 

 Santiago Ramrtn y Cajal, Madrid ; Prof. Emile Picard, 

 Paris; Prof. Hugo Kronecker, Berne; and Prof. George 

 E. Hale, Mount Wilson. 



Lord and Lady Raylf.igh, who have been travelling 

 abroad for several months, have returned to Terling Place, 

 Witham, Essex. 



A Central News message from New York states that 

 Prof. F. L. Tufts, professor of physics at Columbia Uni- 

 versity, was killed on April 15 while testing some electric 

 feed wires. 



The annual dinner of the Institution of Mining and 

 Metallurgy will be held at the Hotel Cecil on Friday, 

 April 30. The president, Mr. Edgar Taylor, will preside. 



The death is reported, at Louisville, Kentucky, of Dr. 

 Letchworth Smith, at the age of thirty-seven. For 

 several years he had been specially engaged in the study 

 of milk, first at Cornell Medical School and afterwards at 

 the research laboratory of the New York Board of Health. 

 He was the founder of the Babies' Milk Fund Association. 



America has lost one of her veteran naturalists by the 

 death of Dr. W. H. Edwards, who was born in 1822, and 

 made a voyage up the Amazon in 1846 to collect objects 

 of natural history. In addition to a volume describing 

 this expedition, he published three series of books on the 

 butterflies of North America. He also contributed to 

 scientific journals a large number of entomological articles. 



By the death of Prof. F. E. Hulme, which was 

 announced in the last number of Nature, botany has lost 

 an assiduous votary. Although his professional career lay 

 outside the subject, as he was for many years professor 

 of drawing on the engineering side at King's College, 

 London, he found time to prepare several popular illus- 

 trated works on flowers. The best known is " Familiar 

 Wild Flowers," published originally in five series, then 

 extended to eight, and a ninth was revised in proof by 

 the author before his death. " Familiar Garden Flowers," 

 produced in conjunction with Shirley Hibberd, was a con- 

 temporaneous publication, and another pleasurable volume, 

 " Familiar Swiss Flowers," appeared last year. The 

 charm of his illustrations lies in the combination of artistic 

 feeling with accuracy of form and colour, while the text 

 discloses an intimate knowledge of plants and flower lore. 



A short essay by Mr. Edward Greenly in the 

 Rationalist Press Association Annual suggests that the 

 ancient Greeks, if they were with us to-day, would be 

 much more likely to favour the teaching of natural science 

 than compulsory Greek in schools. Mr. Greenly points 

 out that the geological observations of Pythagoras were 

 as correct, and his conclusions from them as sound, as 

 those of the founders of modern geology. Archimedes, 

 Aristotle, and Eratosthenes of Alexandria also followed 

 the plain and profitable paths which deviated later into 



