February 27, 1908] 



NA TURE 



401 



which, as he points out, affords a direct comparison 

 between the constant pressure scale of any gas and the 

 absolute scale, but which cannot be applied directly to 

 the constant volume temperatures without knowing the 

 isothermal equation of the gas. He discusses the various 

 empirical assumed formulae for the "cooling effect," and 

 the conclusions deducible from them. The relations of 

 actual gas scales to the thermodynamical scale are set 

 forth, but the author considers that the time is approach- 

 ing when a mere reference of temperatures to " the gas 

 scale " will be insufficient. Mr. Dickson's paper deals 

 with the inversion temperature of the Joule-Kelvin effect 

 both for small and for finite differences of pressure, with 

 special reference to Olszewski's experiments. 



The Physikalische Zeitschrift for February i contains a 

 description, by Dr. C. W. Lutz, of the filament electro- 

 meter invented by himself and Dr. M. Edelmann, jun. 

 The filament consists of a WoUaston platinum wire of 

 about 0001 mm. diameter suspended vertically between two 

 narrow vertical plates, one of which can be put into elec- 

 trical connection with the wire, while the other may be 

 connected either to earth or to some source at constant 

 potential. The repulsion of the filament from the former 

 plate when both are charged is observed through a small 

 microscope magnifying eighty times, and by suitably 

 adjusting the tension of the filament the range of the 

 instrument may be made to extend from 2 volts to looo 

 volts. It is very compact, and its electrical capacity is 

 less than lo cm. 



Mr. C. W. Burrows, of the United States Bureau of 

 Standards, after extensive experiments on the various 

 methods in use for demagnetising iron in magnetic test- 

 ing, comes to the conclusion that the following is the 

 best method of procedure : — the current should be re- 

 versed about twice a second, and diminished at such a 

 rate that the decrease of induction is as nearly as possible 

 the same each second, the process to last about ninety 

 seconds. In obtaining the magnetisation curve of the 

 specimen, the magnetisation current should be reversed 

 about the same number of times, and near the end of the 

 series two throws of the ballistic galvanometer about 

 twenty-five reversals apart should be observed. If they 

 agree, they may be taken as representing the normal in- 

 duction. The next observation may be made by this 

 method without its being necessary to again demagnetise 

 the specimen (Bulletin for January). 



.\ NEW and cheap edition (price 5^. net) of Mr. Benjamin 

 Kidd's " Principles of Western Civilisation " has just been 

 published by Messrs. Macmillan and Co., Ltd. The 

 original work was reviewed at length in N.ature of April 

 24, 1902 (vol. Ixv., Supp., p. vi). In a long introduction, 

 which appears for the first time in the new edition, Mr. 

 Kidd replies to points raised by his critics, and refers to 

 some differences between the evolution of the individual 

 and of a social organism. Mr. Kidd has been appointed 

 to deliver the Herbert Spencer lecture for 190S before the 

 University of Oxford in May or June next. Three lectures 

 have already been given, namely, in 1905 by Mr. Frederic 

 Harrison, in 1906 by Mr. Auberon Herbert, and In 1907 

 bv Mr. Francis Galton, F.R.S. 



OUR ASTRONOMICAL COLUMX. 

 Saturn's Rings. — The January number of the Astro- 

 physical Journal (vol. .xxvii.. No. i, p. 35) contains an 

 article by Prof. Barnard in which he describes and dis- 

 cusses his recent observations of Saturn's rings with the 

 40-incli refractor of the Lick Observatory. On July 2, 



NO. 2000, VOL. 77] 



1907, Prof. Barnard found that, although no direct sun- 

 light was falling on its earthward side, the entire surface 

 of the ring was distinctly visible. On each ansa were 

 two prominent condensations symmetrically placed with 

 respect to the ball. On October 4 — when the earth again 

 passed back to the shadow side of the ring — and for some 

 days after, the ring was perfectly linear, and the con- 

 densations, which, if they were real masses on the ring 

 system, should then have been best seen, had disappeared. 



From his observations Prof. Barnard concludes that it 

 is not merely the illuminated edge of the system which we 

 see when the earth is on the shadow side, but the feebly 

 luminous surface of the ring itself viewed very obliquely. 

 The luminosity is caused by the transmittance, by repeated 

 reflections from the particles comprising the ring, of sun- 

 light. Adopting this interpretation, the condensations are 

 produced by the outer brighter part of the inner ring, the 

 higher illumination of which, as seen ordinarily by directly 

 reflected light, or, as during these observations, by light 

 which had by successive reflections passed through the 

 ring, is probably due to the denser agglomeration of its 

 particles. 



The Objective Prism in Sol.ir Spectroscopy. — A device 

 by which double equatorial refractors, as employed for 

 stellar photography, may be adapted to serve as objective- 

 prism spectroscopes in solar observations, is described by 

 M. E. Schaer in No. 4233 of the Astronomische 

 Nachrichten (p. 137, February 15). The solar rays, pass- 

 ing through the first objective, are, by tw'o reflections by 

 plane mirrors, projected along the axis of the second 

 telescope. Before reaching the second tube the reflected 

 image is, however, intercepted by a slit plate, so that only 

 the narrow beam which passes through the slit traverses 

 the tube to the object glass. On passing through the 

 latter the light falls upon the objective prism, which is 

 silvered on the posterior face, so that after two dispersions 

 and one reflection it passes again through the object-glass 

 and down the tube. The solar spectrum thus produced 

 may be viewed with an ocular, or an arrangement for 

 photographing it may be substituted. By the interposi- 

 tion of a second slit in front of the photographic plate 

 and mechanical movements this instrument may be used 

 as a photospectroheliograph. 



Uniformly Distributed Dark Spots on Jupiter. — In 

 an article which appears in the January number of the 

 Bulletin de la Societe astronoiniqite de France, Mr. 

 Scriven Bolton describes a number of Jovian phenomena 

 observed by him in recent years, and pays particular 

 attention to a series of dark markings which are 

 symmetrically distributed along the northern edge of the 

 south equatorial and the southern edge of the north 

 equatorial bands. As these spots occur in the same longi- 

 tudes on each band and partake of a common motion, Mr. 

 Bolton concludes that they have an objective existence. 

 Generally, the alternate spots on the opposite bands are 

 joined by festoons of dark material which cross the 

 equatorial regions obliquely at angles of 45°. The spots 

 on the southern band present the more marked uniformity, 

 there being twenty-four of them at regular intervals 

 throughout the whole length of this band. Drawings 

 made on June 15, iSgg, November 4, 1903, and February 

 23, 1907, respectively, are reproduced to illustrate Mr. 

 Bolton's description. 



Double-star Observations. — Finding that the published 

 magnitudes of the components of double stars are generally 

 only given approximately. Dr. Joel Stebbins, director of 

 the Urbana Observatory, Illinois, U.S.A., decided to make 

 a number of systematic photometric observations of them, 

 and he now publishes the results in the Bulletin of the 

 University of Illinois (vol. iv.. No. 25, 1907). After 

 describing the instruments employed and the system of 

 observation. Dr. Stebbins gives a catalogue of the 107 

 double stars which he observed, and discusses the probable 

 errors and the differences from the Harvard observations 

 of the same objects. On comparing the results with other 

 available observations, no evidence of variability could, 

 with certaintv, be detected, and in the case of S' Orionis 

 —the Trapezium stars— it appears certain that no change 

 greater than o-o8 magnitude has taken place since the 

 Harvard observations were made in 1878. 



