540 



NATURE 



[December 23, 1920 



The results of recent investigations on the theory 

 of development by Mr. A. H. Nietz, of which Dr. 

 Mees, of the Koilak Research Laboratory, recently 

 gave an account at the Royal Photographic Society, 

 are given in the current (December) issue of the 

 society's Journal. It is found that the "reduction 

 potential" of a developer can be measured by finding 

 the concentration of bromide required to give the 

 same rate of change of depression of density, and 

 this is the method for its estimation that is least 

 subject to error. The relative reduction potentials 

 of sixteen developing agents are given, beginning with 

 ferrous oxalate as 03 and ending with diamidophenol 

 as 30 to 40. The author says that it appears to be 

 well founded that (i) the maximum density tends to 

 increase with increasing reduction potential; (2) no 

 definite relationship can be shown between the time 

 of appearance and the reduction potential, nor is the 

 velocity constant affected by the potential in any 

 regular manner; (3) while the speeds of emulsions 

 vary with the developer employed, they are ap- 

 parently no function of the reduction potential; and 

 (4) the fogging power of a developer also appears to 

 have no relation to the reduction potential. The 

 author also draws conclusions as to the effect of the 

 structure of the molecule of the developer on its 

 reduction potential. The amino-phenols are the most 

 energetic, the hydroxy-phenols come next, and the 

 amines follow. The introduction of a methyl group 



into the nucleus or into an amino-group raises the 

 energy, but two methyl groups are not always more 

 effective than one ; nuclear substitution of a halogen 

 in the hydroxy-phenols raises the energy, and other 

 less general statements are deduced. The growth of 

 the image and of the fog do not generally follow the 

 same law ; evidence was found that fog is practically 

 absent from the high densities and increases as .the 

 image density decreases, but bromide restrains the 

 fog more than it restrains the image. Other allied 

 subjects are considered. 



Messrs. J. Wheldon and Co., 38 Great Queen 

 Street, W.C.2, have just issued a noteworthy catalogue 

 (New Series, No. 91) of books in the various branches 

 of zoological science. It refers to upwards of 

 2000 volumes, classified under the subjects of Protozoa 

 and micro-zoology, Coelenterata, Echinodermata, .An- 

 nelida, Crustacea, Insecta and .\rachnida, Mollusca 

 and Polyzoa, parasitology, evolution, heredity, and 

 hybridity. In addition, there is a list of sets and 

 long runs of scientific periodicals which Messrs. 

 Wheldon offer for sale. 



\. NEW edition of "The Resources of the Sea," by 

 Prof. W. C. Mcintosh, is announced for publication 

 by the Cambridge University Press early in January. 

 The work has been carefully revised and brought up 

 to date. A chapter on the labours of the International 

 Fisheries Council is promised. 



Our Astronomical Column. 



K New Comet.— Mr. Skjellerup, of Cape Town, has 

 discovered a new comet 1920b ; its position on Decem- 

 ber 13 at i2h. 57-4m. G.M.T. was R.A. 8h. ssm. 1607s., 

 S. decl. 9° i' 48'; daily motion + 4m., N. 1° 19'. 

 The comet is moving towards Regulus, and coming 

 into a favourable position for northern observers. Its 

 magnitude at discovery was \o\. It will be remem- 

 bered that Mr. Skjellerup discovered another comet a 

 year, ago; it was, however, unfavourably placed, and 

 very few observations were secured. 



Mr. Van Biesbroeck observed this comet at Yerkes 

 Observatory on December i7d. 2oh. ig-Sm. G.M.T., 

 R.A. gh. i6m. 59-6s.. S. decl. 3° 10' 7". The average 

 daily motion from December 13 to 17 is +5m. 3s., 

 N. 1° 22'. The comet is evidently not very distant 

 from the earth; its motion is direct, and it will pass 

 the ascending node in about ten days. It is visible 

 in a small telescope. 



Tables du Mouvement KfipLfeRiEN. — Ever since the 

 enunciation of Kepler's laws efforts have been made 

 to simplify the determination of true anomaly and 

 radius vector in terms of the time. Many of the 

 methods given are ingenious and useful, but none 

 appear to give so rapid a solution as extended tables. 

 Dr. M. F. Boquet, astronomer of the Paris Observa- 

 tory, has just published a vei^ useful volume with the 

 aid of a grant from the .\cademie des Sciences; it 

 gives for values of e ascending by intervals of 001 

 from 000 to 050, and for values of v ascending by 

 intervals of 1° "from 0° to 180°, the values of M and 

 log r/o to three and five decimal places respectively, 

 together with columns of differences for the variation 

 of V and e. It is thus quite a short com- 

 putation to find V and logr for a given value of M to 

 4" and to the fifth decimal place respectively. 



NO. 2669, VOL. 106] 



Examples are also given showing how the difference- 

 columns may be utilised to obtain seven-figure 

 accuracy by a straightforward computation. These 

 tables will be a boon to all who desire to calculate 

 ephemerides of short-period comets or minor planets. 

 A propos of the latter point, it may be mentioned that 

 the ephemeris of Ceres given in Nature of Decem- 

 ber 9 is found to need the large correction of minus 

 4m. 40S. in right ascension. This large discordance em- 

 phasises the inconvenience resulting from the discon- 

 tinuance of the accurate ephemerides of the four chief 

 asteroids formerly published in the Nautical .\lmanac. 



The Uccle Observatory. — Tome xiv., fascicule iii., 

 of the Annales de I'Observaioire Royal de Belgique 

 shows that a considerable output of work went on 

 at the Uccle Observatory even during the dark days 

 of war. It contains micrometric measurements of 

 172 double stars made with the 38-cm. equatorial by 

 G. van Biesbroeck. The mean result for Castor 

 (epoch 1914142) is 219-59°, 5-30'. The distance shows 

 a marked diminution since about 1890, when the 

 maximum, 576', was reached. So far as it goes, the 

 above observation favoufs Mr. Lewis's minimum 

 ellipse, the period of which is 310 years. 



The Annales also contain a very fine series of 

 cometary observations extending from 1913 to 1919 ; 

 for example, Delavan's comet of T913 was observed 

 for position on seventy-three nights, and its magni- 

 tude determined on thirty-two nights. It remained a 

 naked-eye object for nearly six months, attaining a 

 maximum of 28 magnitude in mid-September, 1914. 

 Among other methods that of extrafocal images was 

 largely used. The comparison stars are thus ex- 

 panded into discs, which renders them more readily 

 comparable with a diffused body like a comet. 



