492 



NATURE 



[March 24, 1898 



'This catalogue has recently been published, so a few words 

 -about the method employed in making the observations may 

 fee opportune. Before setting out on this journey Mr. Stanley 

 Williams made several hundreds of observations to make him- 

 self familiar with this class of work, so that his estimations have 

 ■considerable weight. He adopted the usual method of making 

 variable star observations by using an opera-glass, and bringing 

 ■each star and its comparison stars into the centre of the field 

 ■consecutively. The star ; undergoing comparison was usually 

 compared with two others of known magnitude, one of which 

 was brighter and the other dimmer than the star to be observed. 

 Instead, however, of estimating the difference of brightness 

 between the comparison star and the star under examination 

 in steps or grades, the magnitude of a step being usually 

 different for nearly every observer, he employed another 

 method. This was to mentally divide the interval between the 

 •two comparison stars into as many parts as there were tenths 

 ■of a magnitude between them, the adopted magnitudes of the 

 comparison stars being, of course, known, and then estimate 

 how many of these tenths the star under observation was 

 dimmer and brighter than the comparison stars. 



A step in this case thus corresponded to a tenth of a magni- 

 ■tude on the scale of the " Harvard Photometry." A comparison 

 of the resulting magnitudes of some of the stars observed, which 

 have also appeared in the "Southern Meridian Photometry," 

 shows that " the present catalogue, on the whole, accords 

 exactly with the ' Harvard Photometry,' though the number of 

 stars is too small for absolute certainty." A similar comparison 

 with the " Uranometria Argentina" shows more considerable 

 ■differences, excepting between 2 '8 and 3-4 magnitudes ; but it 

 ^Aiust be remembered that the scale of the " Uranometria 

 Argentina " differs largely from that of the " Harvard 

 Photometry." ■ 



In the course of this work one variable, V Puppis, was 

 •discovered, and thirteen other stars were found to be probably 

 •variable. 



The Variables S Cassiopei/e and S Urs^. Majoris. — 

 Some time ago, in this column (December 2, 1897, p. 105), we 

 ihad the pleasure of saying a few words about the variable stars 

 S Cephei and T Ursne Majoris, which Mr. Peek, of the 

 Rousdon Observatory, had so energetically observed and re- 

 corded during the years 1887 to 1896. We are now able to 

 refer our readers to another small, valuable pamphlet (No. 3) 

 containing the observations, extending over the same years, of 

 the two variable stars S Cassiopeioe and S Ursae Majoris. Each 

 of the observations here recorded is the mean of five visual 

 comparisons with stars whose magnitudes have been previously 

 •determined either by Mr. Peek himself or some other observer. 

 Further, the comparisons are all made with stars in the same 

 .field of view as the variable under observation, the instrument 

 ■employed being a 6 ■4-inch equatorial refractor by Merz. The 

 observations are recorded in a uniform way throughout, in 

 which the date of observation, the magnitude, and remarks as 

 to colour and magnifying power used are given. As in the 

 previous publication, Mr. Peek adds a graphical' study of 

 the light changes of these stars throughout each year, and a 

 perusal of these curves, is of great interest. . We hope Mr. Peek 

 has some more observations of other variables which he will 

 publish in like manner, as it is just such observations that will 

 throw light on the changes which these sta^s undergo. 



OccuLtATioNS Photographically Observed, — Prof. E. 

 'C. Pickering records, in a Circular (No. 26) of the Harvard 

 College Observatory, the result of the occultation of 26 Arietis 

 as observed photographically at that observatory. The instru- 

 ment used was an improved form of that constructed for photo- 

 .graphing the eclipses of Jupiter's satellites, and previously de- 

 scribed. The phenomenon of this occultation was satisfactorily 

 .photographed by Mr. Edward S. King on February 25 of this 

 year. The apparatus was connected with a standard clock, and 

 the photographic plate was moved about 0*03 cm. every time 

 the circuit was closed or opened, two images alternately faint 

 and bright being obtained every second, the duration of ex- 

 posures being 0'o6 and 0'94 seconds. An examination of the 

 series of images showed that the time of occultation could be 

 fixed to within one-tenth of a second. Prof. Pickering adds 

 that by using shorter exposures the uncertainty of the time of 

 ■disappearance can be still further greatly reduced, especially in 

 the case of brighter stars. 26 Arietis is a star of magnitude 6"i ; 

 since satisfactory images were produced in 0'o6 seconds, stars 



NO. 1482, VOL. 57] 



probably down to the ninth magnitude can be thus photograph- 

 ically observed. The stellar images were further examined to 

 inquire whether any lunar atmosphere could be detected by not- 

 ing any change in the intensity of these images ; but none was 

 discovered. A fropos of occultations, it is interesting to draw 

 attention to the fact that Prof. G. P. Bond, more than forty 

 years ago, took a number of photographs of the moon and 

 a Virginis shortly before the occultation of the latter, to deter- 

 mine photographically the position of the moon. 



Comet Perrine. — A telegram from Kiel, dated March 21, 

 informs us that the position of Perrine's Comet at igh. 7m. 

 Mount Hamilton mean time was R.A. 2ih i6m., and Declina- 

 tion 26° 44' north, the movement in these two coordinates 

 being 14 and 37 seconds respectively. 



A MAGNETIC STORM. 



CINCE August 1894 no magnetic storm has occurred in 

 *^ England at all equal to one experienced during the last few 

 days. Its first indication at Kew Observatory occurred about 

 8.55 p.m. on the 14th, when a noticeable increase took place in 

 the horizontal force. This element then oscillated about its 

 normal value to a moderate extent until 4 p.m. on the 15th, 

 when there commenced a large decrease superposed on large 

 oscillatory movements. The minimum was reached about 

 10.48 p.m. on the 15th. During the subsequent rise, which 

 was very rapid at first, there were some further large oscillations, 

 and the element remained somewhat disturbed until 5 p.m. on 

 the i6th. The vertical force was only slightly disturbed until 

 2 p.m. on the 15th. After increasing to a maximum about 

 5 p.m. it decreased rapidly with large oscillations, attaining a 

 minimum about 10.48 p.m. It then reapproached its normal 

 value, the oscillations being large at first, but becoming small 

 early in the morning of the i6th. 



The declination disturbance commenced at the same time as 

 that of the horizontal force, but was small until midnight on 

 the 14th. After a general easterly movement, lasting for some 

 hours, the needle reversed its direction, attaining its extreme 

 westerly position about 2*48 p.m. on the 15th. It then re- 

 commenced a very conspicuous movement to the east, with 

 various large oscillations. After attaining an extreme easterly 

 position about 11. 18 p.m. on the 15th, the needle moved once 

 more to the west, the motion remaining oscillatory. The 

 disturbance did not disappear until about 5 p.m. on the i6th. 



The extreme amplitude of the disturbance was : horizontal 

 force, '0050 C.G.S. units; vertical force, '0057 ClG.S. units; 

 declination, l°26'. In eight minutes, from 10.40 to IC.48 p.m. 

 on the 15th, the horizontal and vertical components exhibited 

 falls of '002 and '003 C.G.S. units respectively. The most 

 rapid change of declination occurred some thirty minutes later. 

 Speaking generally, the most salient features were the large 

 falls ih both the horizontal and vertical components, and the 

 movement of the declination needle to nearly 1° east of its 

 normal position. The storm was presumably associated with 

 the brilliant aurora visible on the night of the 15th in the 

 northern half of the kingdom and in Denmark {Daily Weather 

 Report, March 16). Charles Chree. 



THE AUSTRALASIAN ASSOCIATION. 



. T^HE meeting of the Australasian Association for the Advance- 

 -*- ment of Science, held at Sydney in the beginning of 

 January, appears to have been a very successful one. , From the 

 reports which came to hand a few days ago it appears that the 

 meeting was attended by the foremost men of science in the 

 various Australasian Colonies, and that a large number of 

 papers were read in the different sections. The Association 

 now numbers more than six hundred members. 



The meeting was opened on Friday, January 6, and on the 

 evening of that day Prof Liversidge delivered his address as 

 president of the Association. Saturday, January 7, and suc- 

 ceeding days in the following week were largely taken up with 

 the sectional meetings. Papers were read in connection with 

 astronomy, mathematics and physics ; chemistry, geology and 

 mineralogy, biology, geography, ethnology and anthropology, 

 economic science and agriculture, engineering and architecture, 



