June 30, 192 1] 



NATURE 



565 



captured by the late F. Smith in Devon in 1857, but 

 since that time the species has been lost sight of 

 in this country. Owing to the resemblance which 

 the male bears to a variety of the same sex in 

 Psithyrus rupestris, F., and the similarity of the 

 female to more common Bombi, Dr. Perkins is 

 of opinion that Bombtis pomorutn may have been 

 overlooked, and possibly may be re-discovered by 

 some enterprising entomologist. 



Pamphlet No. 12 (192 1) of the Economic Series 

 issued by the British Museum (Natural History) is 

 written by Mr. F. Laing, and deals with the ubiquitous 

 cockroach. In addition to the common species (Blatta 

 orientalis, L.), three other kinds of cockroach have 

 established themselves in sufficient numbers in this 

 country to be occasionally troublesome. The general 

 reader is far more interested in their control than in 

 their biology, and Mr. Laing finds that a powder con- 

 sisting of three parts of sodium fluoride to one part of 

 pyrethrum is a successful remedy. The mixture 

 should be scattered about the haunts of the cock- 

 roaches in the evening, and the dead ones removed 

 the next morning. The powder is harmless to any 

 domestic pets and is cheaply and easily prepared. 



The inhabitants of Buckinghamshire and Hertford- 

 shire will be grateful to Mr. W. Whitaker for his 

 memoir on the water-supply of the two counties, 

 recently published by the Geological Survey. In both 

 counties chalk is the principal water-bearing rock, but 

 supplies are also obtained from overlying gravels, 

 sands, etc., Tertian,- beds, and the Greensand and 

 Jurassic rocks. The deepest bores recorded are 

 1000 ft., and from some of the wells more than 

 1,000,000 gallons a day are being obtained. Numerous 

 analyses of the water are given, and the details are 

 of considerable interest to all concerned in the well- 

 being of the community. The geological student will 

 be particularly interested in the full description of the 

 swallow holes in which surface-water disappears, and 

 which are numerous in Herts. Probably the best 

 known are those in North Mymms, which can easily 

 be seen at Water End ; here the drainage of some 

 20 square miles of the county is lost. Swallow holes 

 are found in Itwo sets of conditions : along the junc- 

 tion of the Tertiary beds and chalk, and in the chalk 

 itself, where the saturation level is below the bottom 

 of the valley. The former are active at all seasons, 

 the latter may not be. Directions are given for find- 

 ing good examples. There is also an interesting dis- 

 cussion on the effect of pumping on the adjacent 

 wells. 



A PAPER by Mr. S. H. Warren on "A Natural 

 ' Eolith ' Factor>- beneath the Thanet Sand " (Quart. 

 Joum. Geol. Soc., London, vol. Ixxvi., p. 238, 1921), 

 has already raised considerable discussion. It is clear 

 that many persons would have accepted Mr. Warren's 

 naturally flaked specimens as eoliths had their early 

 Eocene age and their mode of origin not been demon- 

 strable. The specialists in eoliths, on the other hand, 

 maintain that the natural product, due to interaction 

 under earth-tremors, is inartistic compared with an 

 eolith for which human origin can reasonably be 



NO. 2696, VOL. 107] 



claimed. Mr. Warren's "natural factory" occurs at 

 Grays in Essex. 



In a short paper of four pages, reprinted from the 

 Proceedings of the U.S. National Academy of Sciences 

 for June, 1920, Prof. A. G. Webster, of Clark Univer- 

 sity, directs attention to a necessary connection be- 

 tween the equation of state of a gas and the specific 

 heats of the gas at constant pressure and at constant 

 volume which does not take the simple form given 

 to it by some authorities. In particular, he shows 

 that a characteristic equation of the form T = pf{v) 

 does not indicate that the two specific heats are in- 

 dependent of the pressure ; on the contrary, neither 

 of them is a constant or independent of the pres- 

 sure, nor is their diff'erence constant, although it is 

 independent of the pressure. Such a gas has no 

 cohesion pressure, although it may have a finite Joule- 

 Kelvin effect. In the same way a gas having a 

 characteristic equation of the form T = vF(p), although 

 it has a zero Joule-Kelvin effect, has specific heats 

 which are neither constant nor independent of the 

 pressure. In conclusion. Prof. Webstef expresses the 

 opinion that the present method of teaching thermo- 

 dynamics by means of the equations of the ideal gas 

 or of the van der Waals equation "is by no means 

 conducive to clearness." 



We have received from the Decimal Association a 

 pamphlet entitled "The High-Value Penny," in which 

 a proposal is put forward to increase the token value 

 of the penny and employ the existing penny, half- 

 penny, and farthing coins to represent values 20 per 

 cent, higher than at present, thus dividing the shilling 

 into ten pence instead of twelve, while leaving the 

 values of the shilling and the ^^ sterling unaffected. 

 All the existing notes and silver coins would be re- 

 tained at their present values, and the sixpenny and 

 threepenny coins employed as half-shilling and 

 quarter-shilling pieces exchangeable into 5 and 25 

 high-value pence instead of 6 and 3 low-value pence re- 

 spectively. At convenience the unpopular silver three- 

 penny piece could be withdrawn from circulation and 

 a more useful nickel twopenny piece issued. It is 

 claimed that by the adoption of this proposal the 

 purchasing power of the penny would be brought into 

 closer harmony with modern needs. Owing to the 

 absence of a coin intermediate in value between 

 id. and igd., the price of articles sold at id. before 

 the war has been increased earlier than necessary to 

 igd., and will be retained longer than necessary at 

 this figure when prices are falling. The chief 

 defects of the recent decimal coinage proposals would 

 be avoided by continuing to reckon in pence instead 

 of in mils, and no new coins or knowledge of decimal 

 arithmetic would be required. 



In the Meteorological Magazine for May Dr. C. 

 Chree gives a brief account of " Recent Work on 

 Aurora." The subject was suggested to him by the 

 installation of an observatory in Shetland, one of its 

 objects being auroral observations. Due acknowledg- 

 ment is made of the work done by Norwegian phy- 

 sicists. Arcs and curtains are said to be the most 

 frequent forms of aurora portrayed, and many, if 



