March 28, 19 18] 



NATURE 



nicroscope. — J. Ritchie : Acetone as a solvent for 

 mounting media. The author claimed for his medium 

 :liat it cleared specimens from various grades of alcohol 

 ■ iirect without the use of essential oils. It did not 

 cause a precipitate or any uneven shrinkage of the 

 tissues of specimens where these had been properly 

 tixed. It did not affect stains such as borax or lithium 

 carmine, Van Giesen's, haematoxylin, Jenner, Leish- 

 man, or Giemsa stains. 



Rontgen Society, March 5.— Capt. G. W. C. Kaye, 

 president, in the chair. — C. R. C. Lyster 

 and Dr. S. Russ : A biological basis for protection 

 against X-rays. In this contribution the study of the 

 protection of X-ray operators was approached from a. 

 somewhat different point of view from that usually 

 adopted. In previous investigations the materials 

 ave generally been tested to ascertain what fraction 

 f the incident rays are transmitted, while in this case 

 an attempt was made to measure the total quantity of 

 radiation received by the operator during, say, a day's 

 work under normal conditions. For this purpose the 

 operator carries a photographic plate upon his person, 

 and at the end of the period under consideration the 

 plate is developed. The density of the resulting image 

 is compared with that of another plate termed the 

 ;■ biological basis plate," which has been exposed under 

 standard conditions of radiation. A preliminary inves- 

 tigation enables the harmful effects of the standard 

 source of radiation to be determined, and thus gives a 

 meaning to the indication of the biological basis plate. 

 Radium forms a useful source of radiation for prac- 

 cal purposes after the initial tests have been made, 

 id it overcomes difficulties in the employment of an 

 -ray tube as a constant source. The effect of hard 

 nd soft radiation (12-in. spark to 2 in.) on the photo- 

 raphic plate was fully investigated, and it was con- 

 uded that for the same ionising effect the hard and 

 )ft rays produced about the same photographic effect; 

 le effect, however, varies with different makes of 

 !ates, and in consequence all comparisons must in 

 I actice be made with the same variety. — H. C. Head : 

 \ mobile X-ray unit. A detailed description illustrated 

 by numerous photographs was given of a motor X-ray 

 unit recently designed and constructed for use in Meso- 

 potamia, etc. The Austin chassis was chosen on 

 account of its low load line, and the body was divided 

 into two portions, one to serve as dark-room, while the 

 rher contained the X-ray equipment. In operation a 

 lit is erected at one side of the car, with the result 

 iiat it is unnecessary to remove the coil or switch- 

 oard for use. Electric current is supplied from a 

 :\ namo run off the motor engine and from a small 

 ittery of accumulators, and is sufficient to render 

 issible the production of short-exposure radiographs. 

 Geological Society, March 6.— Mr. G. W. Lamplugh, 

 president, in the chair.— J. F. N. Green : The igneous 

 rocks of the Lake District. The author first directed 

 rtention to some of the manuscript 6-in. maps of the 

 ake District prepared nearly fifty years ago by the 

 'cological Survey, and pointed out that, although un- 

 lubtedly most accurate, they differed greatly in the 

 >Icanic area from his 'own. He suggested that the 

 ason was that there was a fundamental difference in 

 le classification of tuffs and lavas. A large propor- 

 ion of the Lake District rocks were brecciated, and 

 had been supposed to be altered tuffs. With the un- 

 brecciated rocks into which they passed they had been 

 mapiped as ashes. Recently, manuscripts had been 

 and in the possession of the Geological Survey prov- 

 ig that Aveline, whose maps were extraordinarily 

 • curate and detailed, had anticipated by thirty years 

 le author's separation from the volcanic rocks of the 

 isal beds of the Coniston Limestone Series. When 

 -mapped on this basis, the Borrowdale Series ap- 

 NO. 2526, VOL. lOl] 



peared as a simple and regular sequence, strongly 

 folded, and cropping out in long bands. 



Piiyslcal Society, March 8.— Prof. C. H. Lees, presi- 

 dent, in the chair. — E. A. Owen : The asymmetrical 

 distribution of corpuscular radiation produced by 

 X-rays, (i) The ratio of emergent to incident cor- 

 puscular radiation in the case of the two salts, potass- 

 ium bromide and silver nitrate, has been investigated, 

 when the exciting X-radiations were the characteristic 

 radiations of copp>er, bromine, silver, and tin. (2) The 

 ratio has the same value whether the salt is in the wet 

 or in the dry state. (3) The value of the ratio was 

 found to be approximately the same for each two of 

 the salts, and is equal to 117. This is approximately 

 the same figure as that found by other observers in 

 the case of the metals, gold and silver. — Prof. C. H. 

 Lees: "Air standard" internal-combustion engine 

 cycles and their efficiencies. It is well known that 

 the efficiency of an air standard internal-combustion 

 engine working through a cycle bounded by two adia- 

 batics, and either two isothermals, two constant volume 

 lines, or two constant pressure lines, is given by 

 i_(i/r)7-\ where r is the compression ratio and y 

 is the ratio of the two specific heats of air. In the 

 present paper it is shown that the efficiency is given 

 by the same expression if the cycle is composed of 

 two adiabatics and two curves pv^S., pv^a, where a 

 has any positive or negative value, and A and o are 

 constants. Since o may be chosen so that any explo- 

 sion curve may be followed as closely as desired by 

 short lengths of a curves, a cycle can be drawn with 

 the above efficiency and any prescribed explosion curve. 

 The ratio of the efficiency of a cycle with prescribed ex- 

 plosion and exhaust curves to that of the cycle so drawn 

 is shown to be the ratio of the two areas on the indicator 

 diagram. The thermal efficiency of a cycle with pre- 

 scribed explosion and exhaust' curves is therefore 

 readilv found. 



Optical Society, March 14.— Mr. S. D. Chalmers, vice- 

 president, in the chair.— T. Smith : The detection of 

 ghosts in prisms. Ghosts in prisms are caused by re- 

 flections other than those which form the principal 

 image. Thev are apt to be more serious than those 

 in lenses, inasmuch as a single additional reflection 

 may cause a ghost in a prism, while at least two are 

 necessarv in a lens. Moreover, in lenses the ghost- 

 producing reflections occur at unsilvered surfaces at 

 small angles of incidence, but in prisms the surface 

 may be silvered or the ghost may be produced by total 

 internal reflection Every possible way in which a 

 ghost can arise in a prism may be determined by a 

 suitable development of the prism, or of a section of 

 the prism, on a plane. If a diagram is drawn showing 

 all possible positions of a prism derived from a given 

 initial position, the entire path of any ray within the 

 prism is represented by a straight line, and the devia- 

 tion of the ray is of the constant type if the ray has 

 crossed an even number of lines representing reflecting 

 surfaces, and of the variable type if the number is odd. 



Royal Meteorological Society, March 20.— Sir Napier 

 Shaw, president, in the chair.— Dr. J. S. Owens : The 

 measurement of atmospheric pollution. The need for 

 exact measurements of suspended impurities in the air 

 was explained. The era when a harmless gas like 

 carbon dioxide was taken as a measure of impurity 

 was rapidly giving way to a recognition that the really 

 important thing to measure was suspended dust and 

 dirt. It was shown that the latter connoted great 

 waste of human life, and also of fuel, light, and other 

 important modern needs. As showing the kind of air 

 city dwellers were sometimes obliged to breathe, Dr. 

 Owens gave figures for deposits from the air for one 

 year, April to March, at the following places : — Oldham, 

 1915-16, 950 tons per square mile; Manchester, 1915-16, 



