158 



KNOWLEDGE. 



[July, 1901. 



to freezing-point about the middle of November, an 

 Ice Age woiild be most easily formed when the eccen- 

 tricity of the earth's orbit was at a maximum, and the 

 earth was in ajDhelion about tlie middle of August. This 

 would be the period at which the cap would form most 

 rapidly, but it would no doubt continue to increase 

 in mass for some time afterwaixls, and the most exten- 

 sive cap might be found to corres23ond with an aphelion 

 not at midsimimer but at the^ autumnal equinox. 



I am not at present considering the competence of 

 the caiise assigned by Dr. Croll for the Ice Age in the 

 British Isles. I am only dealing with the dat« of the 

 aphelion which would be best adapted for the formation 

 of a snow-cap. Even with the present small eccen- 

 tricity of the earth's orbit the periods of greatest heat 

 and greatest cold are very perceptibly later than the 

 longest and shortest days. With a more eccentric orbit 

 this diilereuce w-ould probably be increased and the 

 mean tempcratiu-e of England might not fall to freezing- 

 point until a much later date than at present. But 

 whatever this date might be, it is the date at which 

 the sun's distance should be increasing most rapidly 

 in order to produce a lasting snow-cap. 



W. H. S. MoNCK. 



Astronomical. — It is reported that the Harvard 

 College Observatory astronomers, who have been at 

 work in Jamaica, have obtained photographic evidence 

 of the existence of snow on the siu'face of the moon. 

 Details have not yet been received, but it is stated 

 that changes have been detected on many of the moun- 

 tain peaks, and the siniplest supposition is that the 

 variable substance is snow. 



Further reports on the eclipse of May 18th state 

 that good photographs of the corona were obtained 

 by both Mr. Newall and Mr. Dyson, and that Mr. 

 Newall also obtained good results with his gi'ating 

 spectroscope and polariscopic camera, but failed to 

 establish the rotation of the corona. The brightest 

 parts of the corona showed marked polarization. Prof. 

 Barnard's long exposure photographs were unfortunately 

 spoiled by clouds. Count de la Baume Pluvinel, who 

 also obsei-ved in Sumatra, appears to have been pretty 

 successful, though he did not succeed in demonstrating 

 the rotation of th(' coi-ona ; no Fraunhofer lines were 

 detected in the spectrum of the corona. — A. F. 



I ■ I — 



Botanical. — The report of the Departmental Com- 

 mittee on botanical work and collections at the Biitish 

 Museum and Kew, together with minutes of evidence 

 supplied by a number of eminent British botanists, 

 has been published in the form of two Blue books, 

 which contain matter of very considerable importance 

 to all botanists. The Committee was appointed " to 

 consider the ])rcsent arrangements under which 

 botanical work is done and collections maintained by 

 the Trastees of the British Museum, and under the 

 First Commissioner of Works at Kew respectively; 

 and to report what changes (if any) in those aiTange- 



ments are necessary or desirable in order to avoid 

 duplication of work and collections at the two Institu- 

 tions." The recommendations of the Committee are 

 in favour of the union of the two herbaria, and of their 

 being united at Kew, where suitable accommodation 

 would have to be provided for them. It is considered 

 advisable, however, that the fossil plants and the botani- 

 cal objects exhibited to the public at the NatiU'al 

 History Museum should be maintained, .the latter 

 feature to be extended and developed as much as 

 possible. — S. A. S. 



Entomological. — The subject of sound-production by 

 insects continues to attract the attention of naturalists. A 

 valuable paperon "The Stridulating Organs of Waterbugs" 

 has been contributed to the curi-ent number of the Journal 

 of the Qnehett Microscopical Club ( (2) VIII., pp. 33-46, 

 pis. 3-4) by Mr. G-. W. Kirkaldy. He deals principally 

 with the musical performances of the Corixidse. These 

 little insects make a shrill chirping note, which has been 

 attributed by several jirevious observers to the action of 

 a " comb " of regularly arranged teeth on the front foot. 

 But Mr. Kirkaldy maintains that this comb is drawn, not 

 as previously supjiosed, across the edge of the face or 

 beak, but across a special spiny, stridulating area on the 

 opposite front thigh. The arrangement of the teeth of 

 the " comb " varies characteristically in the different 

 species of waterbugs, and Mr. Kirkaldy believes that the 

 elaborated forms of the organ can be derived from the 

 simple row of bristles found on the foot of the tiny 

 Microneta or Sigara. The fully-developed musical instru- 

 ments are confined to the male sex. Another important 

 ])aper on this subject has been lately published by Dr. A. 

 Haudlirsch (Ann. Hofmm. Wien., XV., pp. 127-141, pi. 7), 

 who describes also stridulating organs on the thoracic 

 segments of Reduviids and other land-bugs. — G. H. C. 



Zoological. — Mr. Lydekker's article on " Mammoth 

 Ivory," which ajjpeared in Knowledge for July, 1899, 

 has been republished in the Smithsonian Report for 

 1899, now just issued. 



In the June issue of the Proceedings of the Zoological 

 Society of London, Dr. W. G. Ridewood discusses the 

 structure and origin of the so-called " bonnet " of the 

 southern right whale. This is a lai'ge horny excres- 

 cence, worn into hollows like a much denuded piece of 

 limestone rock, growing on the head of this particular 

 kind of whale probably in the neighbourhood of the 

 blow-hole. More than one somewhat wild tJieoi-y has 

 been suggested to account for its presence. One sug- 

 gestion is that it indicates the descent of whales from 

 rhinoceros-like mammals: another that this species 

 of whale is in the habit of rubbing against rocks in 

 oi'der to free itself from barnacles, and thus produces 

 a kind of com — although why on the nose alone is not 

 st.at-ed ! Dr. Ridewood will," however, have nothing to 

 say to these ideas, but considers that tlie stnicture is 

 due to the fact of the horny layers which are produced 

 all over the skin are not shed on this particular spot. 

 This is satisfactory so far as it goes, but we still want 

 to know the reason for the local retention of these 

 layers and tlieir growth into a kind of horn. 



The brief description of the little known Equiis 

 jfrzevalskii, as represented by a mounted specimen in 

 the museum at Pai-is, in the same journal, cannot fail 

 to be interesting to naturalists. Appai'ontly it may 

 now be taken as certain that the animal in question 

 is really a distinct species, and that in some i-espects 

 at least- — notably the presence of " chestnuts " on all 



