December 12, 1907] 



NA TURE 



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Standards contains an account of a determination they 

 have made by the latter method, according to which the 

 ratio for vacuo is 2-9971 X io'°, with an uncertainty not 

 exceeding i part in 10,000. It is interesting to compare 

 this result with the most probable value of the velocity of 

 light, which, according to M. Weinberg's recent dis- 

 cussion of the measurements available, appears to be 

 iH vacuo 2-9986x10'°, with an uncertainty not exceeding 

 I part in 10,000. 



A METHOD of preserving eggs by dipping them in recently 

 boiled water at a temperature of about 110° F., then into 

 boiling water, and afterwards into cold water, was de- 

 scribed in an article in X.ature of November 28 (p. 84). 

 In reply to an inquiry, the writer of the article states that 

 the time during which the eggs are immersed in the 

 water at 110° F. in this method should be about ten 

 seconds. 



The Silica Syndicate, Ltd., of 82 Hatton Garden, has 

 issued a new price-list of chemical apparatus made from 

 transparent vitreous silica by their special process. The 

 apparatus includes evaporating basins, beakers, crucibles, 

 flasks, retorts, and test-tubes ; the prices are about 75 per 

 cent, lower than those ruling a year ago. and it is antici- 

 pated that as the demand grows for fused silica ware 

 further reductions will become possible. We have had an 

 opportunity of examining the various pieces of apparatus 

 made by the syndicate, and have been struck by their 

 wonderfully clear and homogeneous character as compared 

 with that of silica ware made by other processes. They 

 are, moreover, comparatively thin and light, a fact which 

 makes them useful for many purposes for which coarser 

 vessels would be unsuitable ; crucibles of fused silica, for 

 instance, can often be used in place of platinum crucibles. 

 In spite of their thinness, the quartz vessels are very 

 strong and tough, and much less liable to break than cither 

 ordinary or Jena glass : even if broken they do not splinter, 

 but merely crack, so that they can easily be repaired by 

 fusing the broken parts together. Such repairs are 

 executed by the syndicate at a trifling cost. To those un- 

 acquainted with the properties of fused silica, the following 

 points may be of interest. It does not crack when sub- 

 jected to the most violent and sudden changes of tempera- 

 ture. It is not attacked by acids, with the exception of 

 hydrofluoric acid, and is harder than ordinary glass. Its 

 melting point is approximately that of platinum, whilst it 

 has a coefficient of expansion of 0-00000059 per degree, 

 ihat is, about one-seventeenth the value for platinum. So 

 far as is at present known, it shows no tendency to 

 devitrification. 



.\ NEW catalogue of lantern-slides has been received from 

 Mr. C. Baker, 244 High Holborn, W.C. The list contains 

 slides suitable for the illustration of lessons or lectures on 

 natural history, and includes many from photomicrographic 

 I negatives, as well as photographs taken from nature with 

 an ordinary camera. Sets of slides have also been arranged 

 III illustrate some leading books on microscopic objects. 



Messrs. J. H. Dallmever, Ltd., inform us that they 

 have recently appointed several new wholesale agents for 

 their lenses and apparatus abroad. They state that British 

 lens manufacturers, like British dry-plate manufacturers, 

 are able to hold their own in foreign markets in face of 

 high tariffs walls and severe competition. In the LInited 

 States the duty alone amounts to 45 per cent, of the value 

 nt the goods, whilst Germany is the home of the keenest 

 rnmpetitors of manufacturing opticians. 



We have received from Messrs. Siemens Brothers and 

 I'o., Ltd., two well-produced and conveniently arranged 

 NO. 1989, VOL. •]-j'\ 



catalogues. One deals with thermoelectric pyrometers 

 and temperature indicators and recorders which can be 

 used for all processes in which the accurate determination 

 of temperature between the limits of about —190° C. and' 

 i6oo° C. is a necessary factor. The other supplies a 

 descriptive account, w'ith abundant illustrations, of a great 

 variety of electro-medical apparatus. Among these atten- 

 tion may be directed to the patent tantalum X-ray tubes, 

 which can be worked with the anti-kathode at red heat, 

 and the induction coils with variable primary windings. 

 Medical men and others should find the clear diagrams of 

 assistance in understanding the characteristics of th^ 

 apparatus described. 



Messrs. Newton and Co. have sent us a copy of a 

 descriptive lecture on the moon, illustrated by sixty lantern 

 slides, arranged and prepared by Mr. R. Kerr. The notes 

 upon the characteristic points of the various slides, all of 

 which are from Messrs. Newton's collection, will enable 

 anyone to give an interesting reading on our satellite with- 

 out possessing special knowledge of astronomy. Another 

 pamphlet containing notes on lantern-slides, intended for 

 purposes of popular lectures, deals with general astronomy. 

 This pamphlet is now in its fifth edition, and has been 

 revised and enlarged. It comprises much information of 

 an old-fashioned type, and can scarcely be considered as 

 representing the work and results of modern astronomy ; 

 nevertheless, many instructive notes may be extracted from 

 it. A more careful revision of the pamphlet would have 

 prevented such errors as :— " Of the nature of this ring 

 [of Saturn] . . . we are not acquainted"; 1006 instead" 

 of 1066 as the date of an appearance of Halley's comet; 

 "Mr." Huggins for Sir William Hoggins; and HB 

 instead of H^. 



OUR ASTRONOMICAL COLUMX. 



Photographs of Jupiter's Satellites VI. and \TI. — 

 During the opposition of 1905-6 eighty-six photographs of 

 Jupiter's sixth satellite were secured at the Greenwich. 

 Observatory, with the 30-inch reflector, between August 

 23, 1905, and Februarv 15, 1906. Nineteen photographs 

 of the seventh satellite' were taken between October 22, 

 1905, and January 26, 1906. The opposition of 1906-7 

 was somewhat marred by bad weather, but on twenty- 

 eight nights, spread over a period of 222 days, fifty-six 

 photographs of the sixth satellite were obtained. Only on 

 seven nights, during a period of eighty-seven days, were 

 photographs of the seventh satellite secured, amounting to 

 twelve in all. From these photographs the positions of 

 the satellites were determined, and the results are shown 

 graphically on two diagrams published in the Monthly 

 Notices for November (vol. Ixvii., No. 9, p. 561). The 

 orbits of the four major satellites are shown for compari- 

 son, and the difference in the size of the orbits of the 

 four inner and two outer satellites is very striking. 



Temper.iture Control of Silvered Mirrors. — No. 122 

 of the Lick Observatory Bulletins contains a short paper 

 by Dr. Heber D. Curtis on the temperature control of 

 silvered specula. The writer discusses first the previous 

 records of changes in the focal lengths of large specula, 

 briefly referring to the experience of Profs. Keeler, Perrine, 

 Hale,' and Wright in this matter. He then describes a 

 method of artificial cooling which he has tried, and found 

 to be effective, with the 37-inch Mills reflector, which is 

 being used by the D. O. Mills expedition to the southern 

 hemisphere, of which he now has charge. 



The large mirror has a clear aperture of 36-56 inches 

 and a focal length of 17-46 feet, and, during his work with 

 this instrument. Prof. Wright found that a progressive 

 lengthening of the focal length, amounting to from fifteen 

 to twenty-five millimetres, took place during the first four 

 or five hours of each night's work, the drop in tempera- 

 ture being some 5° C. or 6" C. In the first place. Dr. 



