230 



NA TURE 



[July 6, 1905 



Nos. 4 and 5 of the admirable series of Cold Spring 

 Harbour Monographs are respectively devoted to the life- 

 history of the chrysomelid beetle Chlamys plicata, 

 commonly called " case-bearer," and of the " mud-snail " 

 (dog-whelk), Nassa plicata, E. M. Briggs and A. C. Dimon 

 being the respective authors, or, as some would say, 

 authoresses. The case-bearer is remarkable for the fact 

 that its encased larvae resemble not only undeveloped buds 

 of the alder, but likewise the fruit of the high-vine black- 

 berry. Of the " mud-snail " the life-history and habits 

 are described in considerable detail, and a number of 

 observations recorded with regard to its reactions to 

 light, &c. 



Two addresses, on " Spirals " and " Ambidexterity," 

 which were delivered before the Hampstead Scientific 

 Society by Sir Samuel Wilks, Bart., F.R.S., on April 14 

 and May 12 respectively, have just been issued in pamphlet 

 form by Mr. S. C. Mayle, of Hampstead. The society is 

 to be congratulated on having the active support of so 

 eminent a man as Sir Samuel Wilks. 



At the meeting of the Aeronautical Society of Great 

 Britain to be held on Wednesday next, the following com- 

 munications will be read : — " Some Remarks on Aerial 

 Flight," by G. H. Wenham ; " Demonstration of a Bird- 

 like Flying Machine," by Dr. F. W. A. Hutchinson; 

 "Balloon Varnishes and their Defects," by W. F. Reid ; 

 and " The Thrust of Aerial Propellers," by W. G. Walker. 



OUR ASTRONOMICAL COLUMN. 



Observations of the Satellites of Saturn and 

 Uranus. — An important set of observations of the satellites 

 of Saturn and Uranus, involving some hundreds of 

 individual " settings," was made by Messrs. Frederick 

 and Hammond with the 26-inch equatorial of the U.S. 

 Naval Observatory during 1904. The position angle and 

 distance of each satellite were measured from a second 

 satellite, the angle about the inner body always being 

 taken. The observations extended over the period May 24 

 to October 11, and the detailed results are published in 

 No. 4026 of the Astronomische Nachrichten. 



Geodetic Measurements from Solar Eclipses. — The 

 Journal of the British Astronomical Association (vol. xv., 

 June 22) contains a paper in which Mr. C. E. Stromeyer 

 points out that if the central shadow of the coming August 

 eclipse be accurately located, all the necessary data will be 

 available for the determination of the geocentric difference 

 of any two observation stations. He proposes two methods 

 for eye observations, and two photographic methods, of 

 which one in particular seems capable of being carried 

 out with the desired precision ; it consists in photographing 

 a trail of the central phase of the eclipse on to a moving 

 film. 



The method described can be carried out both within 

 and outside the shadow, but the best results will be 

 obtained if the observer is just on the edge of the shadow. 

 The method can also be used with annular eclipses, and 

 if found to be trustworthy would be a valuable means for 

 gradually determining the geocentric distances of various 

 points, even of islands in mid-ocean, which can never be 

 triangulated. 



Monochromatic Photographs of the Orion Nebula. — 

 On obtaining a series of spectrograms of the Orion nebula 

 with a small objective-prism quartz spectrograph, Prof. 

 Hartmann found that different parts of the nebula emit 

 light of very different composition, whilst large areas, of 

 characteristic forms, shine solely by the ultra-violet radi- 

 ation at \ 3727. This variety of the light emitted by the 

 several areas of the nebula led Prof. Hartmann to employ 

 colour screens in obtaining direct photographs with a 

 Steinheil reflector of 24 cm. aperture and 90 cm. focal 

 length. Three screens were used ; the first completely 

 absorbed all wave-lengths shorter than \ 4S00, but allowed 



NO. 1862, VOL. 72] 



H0 and the two chief nebular lines, N, and N„, to pass 

 through almost without any diminution of intensity. The 

 second screen freely transmitted all radiations between 

 \ 3S80 and \ 3740, but absorbed all others, whilst with 

 the third the absorption commenced at \ 5050. increased 

 rapidly to totality at H/3, extended to \ 4000, and then 

 quickly decreased until at X 3727 the transparency was 

 very nearly complete. In this screen the two chief nebular 

 lines were faintly transmitted, but it was an easy matter 

 to eliminate their action by employing a plate of suitable 

 sensitiveness. Combining the first and third screens cut 

 out HyS, leaving only N, and N, effective. 



Marked differences of the intensities of several areas, 

 as shown on the various photographs obtained with 

 different screens, are plainly seen on the reproductions 

 accompanying Prof. Hartmann 's paper. Evidently the 

 radiation A. 3727 is extraordinarily intense in all parts of 

 the nebula, whilst in some parts it. is almost the sole 

 radiation, producing strong photographic images where 

 the eye sees nothing. The nebula G.C. 1180 surrounding 

 the star c Orionis is scarcely visible on the N, and N\ 

 photograph, but it is a prominent feature on that obtained 

 with the ultra-violet light, and is fairlv bright on the 

 H/3 plate. 



This differential action suggests to Prof. Hartmann the 

 presence of at least three gases in the Orion nebula, one 

 of which emits the chief nebular radiations, the second 

 hydrogen, and a third, which emits the radiation at 

 \ 3727 [Astrophysical Journal, No. 5, vol. xxi.). 



Periodicity of Aerolite Falls. — Among a number of 

 interesting papers published by the Royal .'\stronomical 

 Society of Canada (" Selected Papers and Proceedings," 

 1904) we notice one by Mr. W'. H. S. Monck m which 

 the author suggests that aerolites, like meteors, effect a 

 certain periodicity. He first shows that the months of 

 May and June stand out prominently in his catalogue of 

 aerolites as the two months of the year in which a greater 

 proportion of known falls have taken place. The number 

 per diem for these two months is 1-34, whilst for the rest 

 of the year it is only 081. 



In an argument supporting the suggested periodical re- 

 lation between various aerolite falls, Mr. .Monck cites 

 instances in which (i) aerolites fell within one or two 

 days of each other in the same year; (2) aerolites fell on 

 almost the same date in two consecutive years ; (3) aerolites 

 fell on nearly the same date after an interval of two or 

 three years ; and the number of cases quoted seems to place 

 the matter beyond one of chance coincidences. Further, an 

 analysis of the catalogue dates and numbers indicates a 

 marked tendency for series of falls to congregate about 

 certain dates, and for these falls Mr. Monck tentatively 

 deduces periodicities varying from seven to twenty years. 



The Reality of Supposed Changes on the Moon's 

 Surface. — In a paper published in the June number of 

 the Bulletin de la Sociiti astrononiique de France 

 M. Puiseux discusses at some length the various observ- 

 ations of alleged changes on the lunar surface under the 

 influence of the solar radiation. Going back to the 

 earliest observations of details, he carefully considers each 

 authoritative report of suspected change up to the most 

 recent observations of the reported increase of the diameter 

 of Linn^ during lunar eclipses. Summing up all the 

 evidence thus examined, M. Puiseux arrives at the con- 

 clusion that the case for real changes taking place on the 

 surface of our satellite is not established. He believes that 

 the change of sensitiveness of the retina when observing 

 faint objects is sufficient to account for the changes visually 

 observed, whilst the different conditions of exposure when 

 photographing the eclipsed moon might easily introduce 

 the changes suspected from the examination of photographs. 

 The Circumzenithal Apparatus. — A new circumzenithal 

 apparatus, devised by MM. Nusl and Fric for the deter- 

 mination of latitude, &c., was briefly described in these 

 columns for August 20, 1903. A full and illustrated de- 

 scription of the instrument, and of the various improve- 

 ments suggested by experience in its use, is now given 

 in the Bulletin International of the Acad^mie des Sciences 

 de Fran<;ois Joseph I. (Prague, 1904) by the inventors, 

 together with a detailed account of the observations already 

 made and the methods employed in reducing the same. 



