May 3, 1917] 



NATURE 



193 



In Scientia for January Mr, Philip E. B. Jourdain 

 discusses the function of symbolism in mathematical 

 logic. He maintains that until comparatively recently, 

 symbolism in mathematics and the algebra of logic 

 had the sole aim of helping reasoning by giving a 

 fairlv thorough analysis of reasoning and a condensed 

 forni to the analysed reasoning, which should, by sug- 

 gesting to us analogies in familiar branches of algebra, 

 make mechanical the process of following the thread 

 of deduction ; but that, on the other hand, a great 

 part of what modern mathematical logic does is to 

 increase our subtlety by emphasising "differences" 

 in concepts and reasonings instead of "analogies." 

 He points out the confusion of thought which has led 

 many to believe that mathematical log^ic seeks to 

 displace the free spirit of discovery or invention in 

 mathematics, and the misunderstanding of the par- 

 ticular form of "economy of thought" used throughout 

 mathematics and symbolic logic. He then deals with 

 the function of this kind of economy and the neces- 

 sity of observing the distinction between logic and 

 psychologj', and concludes by sketching some of the 

 results of modern mathematical logic. 



We have received from the Cambridge Scientific 

 Instrument Company List 134, which describes a 

 measuring microscope for workshop use which can 

 be arranged to measure horizontal or vertical lengths 

 up to 4 cm. with an accuracy of ooooi cm. List 191 

 describes a thermo-couple potentiometer capable of 

 reading up to 90 millivolts with an accuracy of a 

 microvolt. List 912 describes the various forms of 

 recording and index thermometers reading up to 

 540° C. They depend on the expansion of mercury 

 enclosed in a steel bulb, a fine bore flexible steel tube, 

 and a Bourdon spiral which actuates the pointer of 

 the direct reading or the pen of the recording form 

 of instrument. 



"Chemistry and Technology of Oils and Fats," 

 P. J. Fryer and F. E. Weston, and "Naval Architec- 

 ture," J. E. Steele, are in the press for appearance in 

 the Cambridge Technical Series (Cambridge University 

 Press). The following works are in preparation for 

 inclusion in the same series: "Architectural Building 

 Construction," W. R. Jaggard and F. E. Drur\% vols, 

 ii. and iii. ; " Electrical Engineering," Dr. T. C. 

 Baillie, vol. ii. ; "Automobile Engineering," A. G. 

 Clark; "Electro-Technical Measurements," A. E. 

 Moore and F. Shaw ; " Paper : Its Uses and Testing," 

 S. Leicester ; " Mining Geology," Prof. G. Knox and 

 S. Ratcliffe-Ellis ; "Textile Calculations — Materials, 

 Yarns, and Fabrics," A. M. Bell; "Laboratory Note 

 Book for Applied Mechanics and Heat Engines," 

 F. Boulden ; " Elements of Applied Optics," W. R. 

 Bower; "Electric Installations," C. W. Hill; 

 "Accounting," J. B. Wardhaugh ; "Chemistry for 

 Textile Students," B. North and N. Bland; "Dyeing 

 and Cleaning," F. W. Walker; "Experimental Build- 

 ing Science," J, L. Manson, vol. ii. 



OUR ASTRONOMICAL COLUMN. 



Persistent Aurora. — By taking advantage of the 

 sensitive si>ectroscopic method of detecting faint 

 aurora. Dr. V. M. Slipher has obtained further evi- 

 dence of a permanent illumination of the night sky 

 by auroral light (Popular Astronomy, vol. xxv., p. 274). 

 A large percentage of the luminosity is concentrated 

 in the yellow-green line about A 5572, and exposures 

 of only a few hours were sufficient to' give impressions 

 with the small spectrograph employed. From June, 



NO. 2479, VOL. 99] 



1915, to November, 1916, upwards 

 were made at Flagstaff on different 

 and the characteristic hne appeared 

 graphs. The observations suggest 

 light is more intense towards the 

 sibly towards the sunrise and sunset 

 but more extensive observations are 

 connection. 



of fifty exposures 

 parts of the sky, 

 in all the photo- 

 that the auroral 

 horizon, and pos- 

 points of the sky, 

 necessary in this- 



A New Catalogue of Double Stars. — An im- 

 portant catalogue of the double stars discovered 

 visually since 1905 has been published as vol. Ixi. of 

 the Memoirs of the Royal Astronomical Societj-. The 

 author is Mr. Robert Jonckheere, a well-known OD- 

 server of double stars, who was director of the 

 observatory of the University of Lille until the events 

 of the war drove him to England as a refugee in 

 October, 1914. The exile thus abruptly forced upon 

 him has given Mr. Jonckheere the opportunity of 

 completing the present catalogue. Most of Mr. 

 Jonckheere 's own observations were made at Lille 

 with an equatorial refractor of 14-in. af>erture, but 

 since his arrival in this country he has made extensive 

 use of the 2S-in. refractor at Greenwich. The cata- 

 logue, however, is not exclusively devoted to the 

 author's discoveries and measurements. It includes 

 all the double stars to the year 1905 which were not 

 included in Burnham's general catalogue of 1906, and 

 all the pairs discovered from that date to the end of 

 1916, the term "double star" here being applied only 

 to those of separation less than 5'. The limit of 

 N.P.D. is 105", and the positions are given for the 

 epwch 1920. The total number of entries is 3950. The 

 catalogue is conveniently planned, and will doubtless 

 greatly facilitate the work of double-star observers. 



Report of Mount Wilson Observatory. — Prof. 

 Hale's report on the work at Mount Wilson during 

 19 16 records new and significant advances in several 

 departments, many of which we have already noted. 

 The first place is naturally given to the spectroscopic 

 method of determining the distances of stars, which 

 is now considered to be established as a fundamental 

 contribution to practical astronomy, and has already 

 afforded valuable confirmation of the conclusions of 

 Russell and Hertzsprung regarding the existence of 

 giant and dwarf stars. Scarcely second in interest 

 is the investigation of periodic spectral changes in the 

 Cepheid variables, which must have a significant bear- 

 ing upon the interpretation of stellar types as well 

 as upon the nature of the variables of this class. 



The use of the new 13-ft. spectroheliograph has 

 revealed the vortex structure about sun-spots in ex- 

 qftisite detail, and certain other investigations have 

 suggested that the forms recorded represent hj'dro- 

 dynamic phenomena rather than lines of force of the 

 magnetic fields underlying the spots. No trustworthv 

 evidence of the .Stark effect in the sun has yet been 

 obtained, but further work on the general mag^ietic 

 field of the sun has confirmed the conclusion that the 

 magnetic axis does not coincide with the axis of 

 rotation; h is inclined at an angle of 5^2°, and 

 revolves in a period of 31-51 days ±062 day. A new 

 map of the sun-spot spectrum has been completed 

 for the region A 6450 to A 6000, and the large scale 

 of i cm. to the Angstrom is sufficient to show the 

 chief Zeeman phenomena. 



Important results have also been obtained in studies 

 of star clusters and nebulae, and in laboratory investi- 

 gations. 



Good progress has been made with the loo-in. re- 

 flector, and it is hoped that this giant instrument 

 will be in actual use in the near future. 



