Oct. 7, 1875] 



NATURE 



497 



i.aving been jg^ro '• ^^ value resulting from the satellite- 

 obsenations is preferred. A further account of this im- 

 portant memoir by the eminent American astronomer is 

 reserved for next week. 



The Minor Planets. — M. Leverrier's Bulletin Inter- 

 national of Sept. 30 mentions the observation of a small 

 planet, on Sept. 21st, by M. Perrotin at Toulouse, 13th 

 mag., which may possibly be new, though at present there 

 is a chance of its identity with No. ']'], which is in the 

 same quarter of the sky and has not been observed since 

 1868, or with No. 137, of which no elements have yet 

 appeared. Its place at 8 P.M. was in R.A. 23h. i6m. 8s., 

 and N.P.D. 95° 12'. 



The Total Solar Eclipse of 1878, July 29. — The 

 American Ephemeris for 1878 is published. The elements 

 of the total eclipse of the sun on July 29, derived from 

 the Lunar Tables of Prof. Peirce, which are adopted for 

 the calculations in that work, are almost identical with 

 those of the Nautical Almanac, founded upon the Tables 

 of Hansen, Denver. Colorado appears to be one of the 

 principal places within the limits of the shadow, though 

 some distance from the central line. The sun will be 

 centrally eclipsed on the meridian, according to the 

 American Ephemeris, in long. 139° 8' W., lat. 60° 32' N. ; 

 and according to the Nautical Almanac, in long. 139° 10' 

 W., lat. 60° 27' N. 



MAYER'S METHOD OF OBTAINING THE 



ISOTHERMALS OF THE SOLAR DISC 

 n^HE short notice which I published of my " Discovery 



-»- of a method of obtaining thermographs of the iso- 

 thermal lines of the solar disc " was so concisely written 

 that the precautions which are necessary in this new 

 method of research were omitted ; but as the republication 

 of my paper in NATURE (vol. xii. p. 301) and in other Euro- 

 pean journals may induce those engaged in astronomical 

 physics to try the process, I think it proper that I should 

 call attention to some very important experimental condi- 

 tions to be fulfilled before accurate results can be reached. 



1. Special precautions must be taken to prevent 

 currents of air from acting on the film of double iodide. 



2. If the image of the sun be formed on the blackened 

 side of the paper, it is absolutely necessary that uniformity 

 should be given to this coating of lamp-black. So diffi- 



cult is this to achieve that I have generally formed the 

 sun's image directly on the film of iodide. Slight irregu- 

 larities in this film do not appear to affect the fomi of the 

 isothermals ; but the latter follow irregularities in the 

 smoked surface. 



3. The most important, and indeed absolutely essential, 

 condition in these experiments is that the image of the 

 sun shall be formed on a truly horizontal surface j for the 

 centre of gravity of any isothermal formed on an inclined 

 surface is always above the centre of the sun's image and 



in a vertical plane passing through this centre. Hence all 

 isothermals thus formed are very excentric when referred 

 to the sun's centre. They are also elliptical. The 

 accompanying figure gives isothermals obtained on an 

 inclined surface. iV .S" is the solar axis. On obtaining 

 these same isothermals on a horizontal surface they were, 

 as near as could be seen, circular and concentric with the 

 sun's image. 



Of the influence of an inclined surface in displacing the 

 isothermals there can be no doubt, and the same action 

 has effected all of the results which have been obtained 

 in the employment of thermopiles in connection with the 

 sun's image received on screens attached to equatorial 

 telescopes. This displacement would mislead an observer, 

 and would cause him to be of the opinion that there existed 

 a decided difference of temperature between the north and 

 south solar poles, and between the portions of the peri- 

 phery of the sun's image near the poles and near the 

 solar equator. Do not these facts reached by me explain 

 the difference in the results obtained by Secchi and 

 Langley ? 



The above effects of inclined surfaces appear to be caused 

 by a film of hot air which flows up over these surfaces, and 

 especially on the lower surface of the screen. If the sun's 

 image is received on a film of iodide enclosed between 

 plates of glass or of mica, the excentricity of the iso- 

 thermals is hardly apparent at first ; but after some time 

 it appears, produced by the action of the ascending film 

 on the surface of the glass. 



The proper method of research is to use a simple 

 Fahrenheit's heliostat with a good plane mirror, and to 

 throw the solar rays in the direction of the polar axis of 

 the instrument. These rays traverse lenses of from 12 to 

 30 feet focus, and just before they have converged to form 

 the solar image they are reflected perpendicularly, by 

 another plane mirror, on to the horizontal surface of the 

 iodide. Alfred M. Mayer 



FA YE ON THE LAWS OF STORMS* 



Examination of the Theory of Aspiration. — After a 

 somewhat detailed account of opinions held regarding 

 waterspouts in the prehistoric and Roman epochs, and 

 from the sixteenth century downwards, all agreeing in this, 

 that the water of the sea is sucked up to the clouds by these 

 meteors (Fig. 6), M. Faye inquires. How then could it be 

 doubted that waterspouts, and consequently tornadoes, 

 typhoons, &c. are simply phenomena of aspiration .?f Such 

 has been in reality, since the time of Franklin, the point 

 of departure for meteorologists ; and hence the prevailing 

 notions regarding hurricanes, that they are centripetal and 

 formed by horizontal currents of air flowing from all 

 quarters towards the centre of aspiration. 



Clearly in this case the concUisions have not been 

 drawn with the caution which science demands. To 

 accept, with the eyes shut, the most astounding assertions 

 without examination or verification ; to believe, for ex- 

 ample, that a waterspout could suck up the water of the 

 sea to a height of 2,000 feet when the most powerful 

 pump could not raise it to the height of forty feet ; to 

 admit that insubstantial vapours could form a tube whose 

 sides are capable of resisting the whirling masses of 

 water supposed to ascend through it ; to assert that 

 deluges of sea- water are engulphed in the clouds where 

 the clouds cannot retain simple drops of rain, is not 

 in accord with the usage of science, and indeed can only 

 be explained by the dominating power of an old prcju- 



* Continued from p. 459. 



t It not being considered as disputed that a tornado is nothing but a large 

 waterspout, a typhoon only a large tornado, and that there is no essential 

 difierence between a cyclone and a typhoon, M. Faye proceeds to test the 

 theory of centripetal aspiration as regards waterspouts and tornadoes, and 

 conceives that the conclusions thus arrived at will have equal weight when 

 applied to the theory of cyclones. 



