March i, 19C0] 



NATURE 



433 



mined by further researches whether this condition was unique 

 at any particular pressure and teniperature in the saturated 

 steam. 



When saturated steam is wiredrawn by free expansion through 

 a small orifice, if the pressure in the wiredrawn steam be 

 sufficiently reduced, the steam will become superheated, and, if 

 the flow through the orifice is truly adiabatic, the total energy 

 per lb. cf steam is the same on both sides of the orifice. Now, if 

 the energies of motion be made sufficiently small, this energy will 

 exist as heat, and, assuming the steam before passing the orifice 

 to be in the same condition as that exf)erimented on by Regnault, 

 its total heat energy above that of water at 32° F. is known, and 

 hence the total heat of gasification of the superheated wiredrawn 

 steam from water at 32" F. is known. If, therefore, we observe 

 the pressures and temperatures in superheated steam wiiedrawn 

 from definite initial saturated conditions, simple calculations 

 will suffice to give various values of the specific heat at constant 

 pressure in superheated steam. 



In the experiments, the author obtained adiabatic flow by 

 using orifices drilled in pieces of plate glass. The temperature 

 and pressure of saturated steam in a steam chest, in which a 

 constant supply of steam is kept, are taken, the steam is then 

 drawn upwards to the orifice, and, after wiredrawing, its 

 pressure and temperature are again taken, using for the deter- 

 mination of the latter a thermoelectric junction immersed in 

 the steam. 



The results of the experiments show that saturated steam at 

 any particular pressure, obtained by relieving it of suspended 

 moisture by gravitation, has only one condition as toils dryness, 

 and the total heat of evaporation of steam so obtained is that 

 given by Regnault's experimental results. 



It is further shown that steam obtained 



in this manner has not the maximum 

 density at that particular pressure and 

 temperature of saturation, there being still 

 an eflect as if a small quantity of moisture 

 remained in the steam, which would re- 

 quire removal by further application of 

 heat at the same temperature before the 

 steam would become superheated, thus 

 showing that the latent heat of such 

 steam as given by Regnault's results, has 

 not its maximum value. 



It was also found that by an application 

 of Prof. Reynold's method of determining 

 the perfectly gaseous condition of steam, 

 under ordinary pressures and temperatures, 

 no indications of that condition of steam 

 known as a perfect gas were even ap- 

 proximately obtained, and that Rankine's 

 formula 



H = no-ff(T-32) 

 for the total heat of gasification H of 

 superheated steam at a temperature T 

 (Hfl being the latent heat of formation of 

 steam at 32" F. ), which was formed on 

 the assumption that such a perfect gas 

 condition did exist in steam, could not be 

 applied to superheated steam. 



The mean specific heat under constant pressure was obtained 

 for various pressures and between various temperatures, showing 

 a wide range of variation in its value with temperature. Thus, 

 at atmospheric pressure the mean Kp between 230° F. and 

 246"-5 was 0-4317, and between temperatures of 295° and 

 3ii°5, Kp was 06482. 



The specific heat Kp was found to be independent of the 

 pressure, but to vary very nearly as the fourth power of the 

 absolute temperature. 



If d — ^ ) denote the cooling eff"ect produced by free expan- 

 sion, the following formula, which is thermodynamically correct, 

 viz. : 



... .(I) 



(2) 



By integrating Thomson's formula 



^= '''^^ 

 T zz + fKp 



for the cooling effect c, and using the experimental value of th f 

 product fKp obtained, values of the specific volumes {v) o 

 superheated steam at various pressures and temperatures were 

 calculated, the lower limit of integration being taken from the 

 known data in the saturated condition of steam. 



It follows from equation (i) that, for any gas in which Kp is 

 independent of the pressure, and this is so for many gases, 

 formula (2) must be capable of direct integration in the form 



where y{/) denotes any function of the pressure. 



February i. — *' A Case of Monochromatic Vision." By Sir 

 W. de W. Abney, K.C.B., F.R.S. 



The patient, K. B., was aged twenty-five, and the notes of 

 his case are as follows : — Vision always defective ; has always 

 been colour blind. Has quick horizontal nystagmus ; probably 

 an absolute central scotoma. He is always "day blind." His 

 vision for right and left eyes is 6/60. He is not night blind. 

 His fields are nearly, but not quite, full for white. He shows 

 no definite changes in his eyes. As to his luminosity curve, 

 he matched all colours with white, and with the same facility as 

 if they were white. 



In the accompanying diagram the curve shows the luminosity 

 of the spectrum to the patient K. B. and also of a previous case, 

 P. , together with the curve of luminosity for the normal eye. 



t B 10 It » 16 la 



kM-frH 



enables a check to be made on the experimental results, for if 

 Kp is independent of the pressure, the product cKp must be 

 independent of the temperature. In the experiments, the 

 product cKp was found to be independent of both pressure 

 and temperature. 



NO. 1583, VOL. 61] 



I ££M ibesaox o^m •?« J^« '**'^ ^s m^ 64 S6 



As regards the first two, it will be seen that the maximum of 

 each curve is about scale number 40, or close to e. On the 

 right-hand side of the maximum the curves do not absolutely 

 agree. K. B.'s observations were first made in the red and 

 green, and his readings at first were not very close, and a mean 

 had to be taken. As the colours he had measured went towards 

 the blue his measures were much more accordant, as he had be- 

 come accustomed to the methods employed. The slight diver- 

 gence on the left-hand side of the curve from that of P is 

 probably due to his colouring matter in the yellow spot. 

 Attention must be again called to the fact that these curves are 

 practically identical with those obtained by the normal eye when 

 It measures a spectrum of very feeble luminosity, and also agrees 

 with the results obtained by measuring the diminution of each 

 ray when it first becomes invisible, and making a curve of the 

 reciprocals of the numbers, taking the highest point of it as 100. 

 Physical Society, February 23.— Prof. S. P. Thompson, 

 F.R.S. , Foreign Secretary, in the chair.— Prof. R. W. Wood, 

 of the University of Wisconsin, U.S.A., exhibited and described: 

 (I) Photographs of sound waves and the kinematographical 

 demonstration of the evolutions of reflected wave-fronts. The 



