October 20, 1923] 



NATURE 



603 



in the intensity of solar radiation in the temperate 

 zone. Observations are used for as many stations as 

 practicable in the United States, and in using the 

 published means of temperature derived from the 

 daily extrerries, appropriate corrections have been 

 applied to reduce to true means. Temperatures 

 dealt with range between the years 1750 and 1921, 

 but the number of stations are very few prior to 1825. 

 Summarising the conclusions and results of various 

 authorities on the subject, the author states that it 

 appears that the weight of evidence is in favour of 

 the existence of a variation in the air temperature of 

 the globe corresponding roughly with that of the 

 spottedness of the sun, an increase in spots corre- 

 sponding with diminished terrestrial temperature and 

 vice versa. The effect is best shown in the tropics 

 and is difficult to trace in temperate latitudes. There 

 were three pronounced maxima and minima of tem- 

 perature between 1873 and 1921, the maxima occur- 

 ring in 1878, 1900, and 1921, and minima in 1875, 

 1893, and 1917. 



Bombay Magnetic Curves'. — ^We have received 

 from the Director of the Government Observatory, 

 Bombay, a collection of photographic copies of 

 Bombay magnetic curves for selected disturbed days 

 during the years 1906 to 191 5. Records are included 

 from several hundred days, covering about 150 large 

 sheets. Magnetic disturbance at Bombay is seldom 

 large except in H, the intensity of the horizontal 

 component. The curves reproduced are mostly for 

 this element, but the declination and vertical force 

 curves are also reproduced for some of the storms. 

 The times, and the base line and scale values, are 

 clearly shown in every case, and the reproductions 

 are excellent ; thus much valuable information is 

 deducible as to the character of magnetic disturbance 

 in Bombay. As compared with curves from European 

 or North American stations, the Bombay curves are 

 comparatively free from rapid oscillations. Some of 

 the curves, however, are decidedly lively, including 

 those for February 9-10, 1907, September 12-13, 1908, 

 May 14-15, 1909, September 25, 1909 (when there 

 was considerable loss of trace), and June 17, 1915- 

 There are many examples of " sudden commence- 

 ments " of magnetic storms, all or nearly all exhibiting 

 the characteristic rapid rise of horizontal force. In 

 some cases this increase of force persists for a number 

 of hours, the curve having a crested appearance ; 

 in other cases a fall to less than the normal value 

 follows hard on the initial rise. The weight of the 

 volumes of collected curves is considerable, and the 

 Director of Bombay Observatory expresses his regret 

 that owing to the heavy postage, and the necessity 

 for economy, he has been obliged to restrict the issue. 

 :He would be glad, however, on receipt of the postage, 

 to send a copy to any magnetician who would like 

 'to have one. 



Coconut Oil. — The coconut oil industry is sur- 

 veyed in the Chemical Trade Journal for September 7. 

 This substance is known to us as a fat ; only in 

 warmer climates is it an oil. It is obtained from the 

 kernels of the fruit of the coconut palm, which 

 flourishes in India, Ceylon, and other tropical coun- 

 tries. The first importations into Europe occurred 

 in 1815 ; they have since steadily increased. The 

 article contains brief accounts of the properties 

 (physical constants, etc.), composition, and manu- 

 facture of the oil. The bulk of the oil is used in 

 the soap and candle industry. Future prospects are 

 discussed. 



A Direct Reading X-ray Spectrometer. — In 

 1915 Duane and Hunt found that a spectrum of 



NO. 2816, VOL. I 12] 



general X-rays is terminated sharply at the short 

 wave end, the boundary wave-length being precisely 

 connected by Planck's quantum relation with the 

 maximum voltage applied to the X-ray bulb. The 

 output of general X-rays is roughly proportional to 

 the square of the voltage, and provided the peak- 

 voltage is the same, the energy-distribution curve 

 of the X-ray spectrum is found not to vary markedly 

 with the shape of the wave-form of the exciting 

 potentials which obtain in practice, whether from 

 coil or transformer. For medical purposes, at any 

 rate, it is sufficient to assume that in the absence of 

 a filter the general quality of the rays is independent 

 of the means by which the X-rays are generated but 

 is determined only by the position of the quantum 

 limit. Drs. Staunig, March, and Fritz, of Inns- 

 bruck, have designed a convenient type of X-ray 

 spectrometer for measuring this boundary wave- 

 length. In this instrument (the English agents for 

 which are Messrs. Schall and Son, 71 New Cavendish 

 Street, W.i) a narrow slit of X-rays passes through a 

 thin plate of rock salt crystal and the deviated beam 

 is observed visually as a narrow band on a fluorescent 

 screen provided with a scale of wave-lengths. The 

 crystal is capable of rotation, and the observations 

 consist essentially in measuring the minimum devia- 

 tion between the reflected beam and the undeflected 

 beam. In practice it is convenient to ascertain both 

 the right-hand and left-hand positions of the deflected 

 beam and halve their angular separation, thus avoiding 

 a determination of the zero position. It is important 

 that the observations should be made in a darkened 

 room by an eye thoroughly adapted to darkness. 

 The spectrometer, which .should be earthed, is brought 

 as near the X-ray tube as possible, the protection 

 for the operator being afforded by sheet lead. As 

 will be gathered, the instrument is also capable of 

 being used as a means of measuring peak-voltage. 



Temperature of the Crookes Dark Space in 

 Glow Discharge. — Herr R. Seeliger, in the issue of 

 the Zeitschrift fUr Physik of June 29, contests the 

 opinion recently expressed by Giinther-Schulze that 

 the temperature in the dark space of the glow dis- 

 charge is high (Nature, October 13, p. 557). The 

 canal ray particles are in part neutral, and do not 

 behave like elastic spheres to which the geometrical 

 laws of mechanical collision can be applied. When 

 collisions take place in which the charge is altered, 

 the changes of velocity and of direction are small ; 

 when the colliding particles are absorbed, this takes 

 place without previous appreciable loss of velocity. 

 It IS only for the first type of collision that the free 

 path is of the same order as the molecular free path ; 

 for the second it is very much greater. For ionic 

 velocities, with high or " anomalous " cathode drop, 

 these properties of the canal rays can probably be 

 directly applied to the glow discharge ; for smaller 

 values, corresponding to normal cathode drop, 

 similar complete observational results are not avail- 

 able. Certain qualitative observations {e.g. those of 

 Dempster) point to the fact that things are essentially 

 the same in both cases ; and observations made so 

 far on canal rays ( + ions) do not suggest the existence 

 of the difficulties raised by Giinther-Schulze ; but 

 seem rather to be in agreement with the results 

 obtained by him as to energy relations and distribu- 

 tion of velocity, without assuming a high temperature 

 in the dark space. All direct measurements of the 

 temperatures of the cathode, and of the dark space, 

 have shown that these are only a little higher than 

 that of the surroundings, not much more than loo" C, 

 although in special cases the temperature of the 

 cathode can be raised to the melting, or even the 

 vaporisation, point. 



