NATURE 



. [July 17, 1890 



tinuous spectrum, the usual flame comparisons being employed if 

 necessary. In the General Catalogue the following description is 

 added : — " A very remarkable object ; very bright ; exceedingly 

 large ; extremely irregular figure ; with large cluster." Webb 

 refers to it as "a splendid galaxy object, visible to the naked 

 eye." 



(2) This nebula was discovered by Tuttle in 1859, and, 

 according to D'Arrest's observations in 1863, it would appear to 

 be variable. It is oval in shape, 2' long and 80" broad, and is 

 said to be "pretty bright." No attempt has been made, as far 

 as I know, to determine its spectrum, to say nothing of any 

 variations of spectrum which may accompany the supposed 

 changes in brilliancy. 



(3) This star is one of Group II, at a very late stage. Duner 

 states that " the bands 2, 3, 7, 8 are visible, but they are diffi- 

 cult to recognize as bands, because of their little width. The 

 spectrum is almost of the same type as that of a. Tauri." A 

 special study should be made of the lines which accompany the 

 bands, with special reference to how they differ either in position 

 or intensity from the darkest lines in the solar spectrum, 



(4 and 5) According to Vogel, these stars have very well 

 developed spectra of the solar type and of Group IV, 

 respectively. 



(6) The spectrum of this star is a well-marked one of Group 

 VI., the principal bands being very wide and dark. There is 

 possibly also a trace of band 4 (A 589). 



(7) This variable will reach a maximum about July 24. Its 

 spectrum is of the Group II. type, and is stated by Duner to be 

 one of the finest in the heavens. The range of variation is 

 small — 4 -3-4 '6 — in a period which is not yet completely deter- 

 mined (46 ? days, according to Gore). Observations similar to 

 those suggested for other variables of the same type should be 

 made. A. Fowler. 



Photographs and Drawings of the Sun.— The Memoirs 

 of the Royal Astronomical Society, vol. xlix. Part 2, 1887-89, 

 have just been issued, and contain, with other papers, one pre- 

 sented by the late Father Perry in June 1889 on the above 

 subject. 



The areas of spots derived from the solar photographs of 

 1887, and published in the " Greenwich Observations," have 

 been compared with similar values computed from the measures 

 of the drawings made at Stonyhurst College Observatory, 

 The area computed from the photographs, however, shows a 

 decided general excess over those obtained from the drawings. 

 An idea of the difference may be obtained from the values of 

 the mean daily spotted area, that for 1887 taken from the 

 photographs being 179, while the drawings give 171. 



On 29 days penumbra are found in the drawings and not in 

 the photographs, whilst such records occur on the photographs 

 alone only 16 times ; hence the greater area obtained from the 

 photographs cannot be explained by a failure in the drawings to 

 record faint spots and penumbral markings. 



An attempt was made to compare the faculae recorded on the 

 drawings and on the photographs, but unsuccessfully, owing to 

 the enormous excess obtained from the former over that com- 

 puted from the latter. To eliminate this difference Father Perry 

 suggested that the conditions necessary to obtain good photo- 

 graphs of faculte may differ from that which is best for spots, 

 and that, therefore, a twofold series of photographs may be 

 necessary, one for spots and the other for faculse. Two plates, 

 showing sun-spot drawings in 1887, from the Stonyhurst series, 

 accompany the memoir. 



Observations of the Zodiacal Light.— Prof. Arthur 

 Searle, in Astron. Nachr., No, 2976, contributes a note on 

 zodiacal light observations made at Harvard College Observa- 

 tory during the last fifty years. With respect to the permanence 

 of the ordinary western zodiacal light, the observations support 

 the results obtained by previous observers, viz. that it must be con- 

 sidered as a very permanent phenomenon, and one subject only to 

 slight variations in its degree of visibility, apart from atmo- 

 spheric causes. Another principal subject of investigation was 

 the normal distribution of light in the zadiac and its vicinity, 

 and it is noted that the zodiacal bands, apparently forming a pro- 

 longation of the ordinary zodiacal light, were never seen at 

 Harvard College. A number of permanent bands or belts of 

 faint light, however, not confined to the zodiac, although certain 

 portions of them follow the course of the ecliptic, are described 

 in the records. A comparatively large number of observations 

 of the phenomena of a feeble maximum of light in opposition to 



NO. 108 1, VOL. 42] 



the sun, commonly known as Gegemchein, have been obtained. 

 Prof. Searle thinks that the photometric observations of Muller 

 and Parkhurst, which show that as an average asteroid ap- 

 proaches opposition its brightness increases by about 003 of a 

 magnitude for every degree by which its phase is increased, may 

 afford an explanation of this slight maximum of light in opposi- 

 tion to the sun, the light being reflected in this case from the 

 meteoritic matter dispersed through the solar system. Indeed, 

 if the amount of light received from a meteoritic particle be 

 supposed to increase even proportionally to its phase, a maximum 

 appears at opposition, while the law of increase in light 

 assumed for the asteroids, was approximately proportional to 

 the fourth power of the phase. 



Ring Nebula in Lyra.— The current number of Comfles 

 rendus (July 7) contains a note byM, G. Rayet on a photograph 

 of this nebula obtained at Bordeaux Observatory with an ex- 

 posure of three hours. The photograph shows all the stars 

 observed near the ring by Lord Rosse in 1844 ; the star with the 

 signification 3, however, is double, whereas that astronomer, 

 and later Prof. Hall, mapped it as triple. There is also 

 a very definite indication of a nebulous star of the 14th or 15th 

 magnitude, almost in the centre of the ring. Although this star 

 has been observed by many astronomers {e.g. Hahn, Secchi, 

 Lassell, Schultz, and Holden) and has been photographed by 

 Gothard, other astronomers (viz. Herschel, D' Arrest, Lord Rosse, 

 Hall, and Vogel) have observed the nebula when the star was 

 not visible, and it does not appear on the photographs taken by 

 the Brothers Henry previous to 1886. M. Rayet therefore con- 

 cludes that the star is variable, and hopes to make such observa- 

 tions and obtain such photographs as will enable him to demon- 

 strate the fact. Stars in or near nebulas and clusters seem from 

 recent investigations to be more subject to variability than those 

 not so situated. 



Photographs of Stellar Spectra.— In the same number 

 of Comptes rendus a note occurs by Admiral Mouchez, on some 

 photographs of stellar spectra taken by the Brothers Henry at 

 Paris Observatory, and presented by him to the Academy. 

 Some of the photographs were obtained by means of a prism 

 having an angle of 45° placed in front of the object-glass of 

 the photographic equatorial, others by means of a prism having 

 an angle of 22° ; and Admiral Mouchez remarked that, although 

 the results represented the first attempts in this direction, they 

 compared very favourably with those obtained in America, 

 where work of the same nature has been carried on for some 

 time. It is noted that the Brothers Henry attribute the fuzziness 

 of the lines in the spectra of stars like Altair to a high velocity 

 of rotation and a great amount of agitation at the surface. The 

 photographs are the beginning of an investigation into the che- 

 mical composition of stars and motion in line of sight, recently 

 begun at this Observatory, 



ON THE SUPERFICIAL VISCOSITY OF 

 WA TER?- 



HTHE idea that liquids are endowed with a viscosity peculiar 

 to the surface is to be found in the writings of Descartes 

 and Rumford ; but it is to Plateau that its general acceptance is 

 due. His observations related to the behaviour of a compass 

 needle, turning freely upon a point, and mounted in the centre 

 of a cylindrical glass vessel of diameter not much more than 

 sufficient to allow freedom of movement. By means of an ex- 

 ternal magnet the needle was deflected 90° from the magnetic 

 meridian. When all had come to rest the magnet was suddenly 

 removed, and the time occupied by the needle in recovering its 

 position of equilibrium, or rather in traversing an arc of 85°, 

 was noted. The circumstances were varied in two ways : first, 

 by a change of liquid, e.g., from water to alcohol; and, 

 secondly, by an alteration in the level of the liquid relatively to 

 the needle. With each liquid observations were made, both when 

 the needle rested on the surface, so as to be wetted only on the 

 under side, and also when wholly immersed to a moderate depth. 

 A comparison of the times required in the two cases revealed 

 a remarkable dependence upon the nature of the liquid. With 

 water, and most aqueous solutions, the time required upon the 

 surface was about double of that in the interior ; whereas, with 



' Paper read before the Royal Society, by Lord Rayleigh, Sec.R.S,, on 

 June 5, 1890. 



