Oct. 24, 1878] 



NATURE 



669 



May 15. 



A.M. 



1. 15. — Weather wet. High winds coming on. 

 7.0. — Nearly six hours' rain and wind. 



The numbers 199, 20D, 201, and 202 are those of the wires. 



Mr. Ellis has also told us (p. 641) of what was observed at 

 Greenwich. Although the magnetic disturbance commenced 

 about 6 P.M. at Greenwich, it only reached a maximum at 

 9 P.M., when the electric disturbances were observed at Haver- 

 fordwest, though indifferent working, most probably due to 

 them, commenced at 6,40. At n.45 p.m. the north end of 

 the needle at Greenwich moved sharply westward, and about 

 the same time the currents were reversed at Haverfordwest. 

 From midnight to 12.40 A.M. the currents gradually disap- 

 peared. Earth currents were also active at Greenwich, as 

 indeed they were everywhere. Unfortunately the wires at the 

 post-office were so fully occupied with press work during these 

 hours, that no observations could be taken. It will be noticed 

 that the aurora borealis was observed. "W. H. Preece 



October 21 



Giddiness 



A TRUE theorj' of the cause of giddiness ought to explain the 

 following extreme experience, which deserves record in print. 

 The method was first told to me by a friend ; I once tried it 

 myself successfully in a mitigated form, and will assviredly not 

 repeat the experiment, and I persuaded a philosophical friend 

 to try it also, with much the same result. Stand in the middle 

 of a soft field where you can't hurt yourself by tumbling on the 

 ground or against anything ; avoid having your best clothes on, 

 and secure appreciative spectators. Then put both hands one 

 above the other on the top of your umbrella or walking-stick, 

 and bend down until your forehead rests on the back of your 

 hands. Thus your legs will be vertical, your body will be more 

 or less horizontal, and the umbrella will be vertical. Shut your 

 ■eyes. Then get a friend, by touching your hips, so to guide 

 you that you shall circle three times, with a sidelong gait, round 

 the vertical umbrella as an axis. Finally raise your head quickly, 

 and try to walk straight as though nothing particular had hap- 

 pened. What will occur is a frightful giddiness and feeling of 

 sickness, a sense of the ground rising up tumultuously on all 

 sides, a wild rush to save yourself, and a headlong tumble. 



F. G. 



OUR ASTRONOMICAL COLUMN 



The Saturxian Satellite Hyperion. — In a letter 

 from Prof. Asaph Hall it is remarked that the ephemeris 

 for September last, given in Nature, requires correction 

 by nearly two days, although it was deduced from the 

 elements which he showed to closely represent the 

 Washington observations in 1875 ^i^d ^876 {Asiroii. 

 Nach., No. 2,137). There appear to be great difficulties 

 attending the satisfactory detennination of the orbit of 

 this satellite, doubtless arising in the main from the 

 magnitude of the perturbations with which its motion is 

 affected, but for this reason it is the more necessary that 

 it should be regularly observed, and a rough indication of 

 the position of so extremely faint an object is better than 

 none. 



If we take for a peri-saturnium passage September 

 24-8393 G.M.T. with Prof. Hall's other elements, the 

 •calculated and observed distances on September 27 agree, 

 and the computed angle is one degree in excess of obser- 

 vation. On the same system the following angles and 

 distances are found for loh. G.M.T. : — 



Angle. Distance. 



Angle. Distance. 



Nov. 



The IVIean Parallax of a Star of First IMagxi- 

 tude. — Prof Gylden, director of the Observatory at 

 Stockholm, has reported the result of a preliminary cal- 

 culation bearing upon the mean distance of a star of the 

 first magnitude. Remarking that in the actual state of 

 our knowledge, when a general result is to be deduced 

 from the parallaxes so far measured, we must not only 

 take into account the apparent brightness of the stars 

 concerned, but also their apparent proper motions, since 

 the magnitude of the proper motion is to be viewed as at 

 least as sure a criterion of a measurable parallax as the 

 apparent brightness ; as a hypothesis, it is then assumed 

 that the actual parallax ^ of a star of «th magnitude 

 with the apparent motion s, will be given by the formula 



/ = P 



<T„ M„ 



where <7„ signifies the mean apparent motion of a star of 

 «th magnitude and M„ the distance estimated according 

 to its brightness. P is a constant, which for M = i indi- 

 cates the mean parallax of a star of the first magnitude. 



Prof. Gylden takes the following data, depending upon 

 observation, for sixteen stars, of which the parallaxes are 

 supposed to be known with the greatest degree of ap- 

 proximation : — 



From the adopted values of /, s, together with the 

 products cT;, M„, 16 equations of condition can be formed, 

 the solution of which by the method of least squares will 

 furnish the value of P. But Prof. Gylden points out that 

 this mode of treatment will not be found to answer the 

 object in view, since the determination of the weights of 

 the different equations, which can in no wise be consi- 

 dered equal, is attended with great difficulties. On the 

 assumption of equal weight, the value of P comes out, 

 o"*048. As another mode of treatment, normal equations 

 may be formed in various ways, each containing the 

 unknown quantity P, and consequently each serving for a 

 determination of the quantity sought. The sum of all 

 the equations thus obtained gave P = o'''*o62. 



This value, however, is greatly influenced by several 

 stars of the first magnitude with large proper motion. 

 Omitting a Centauri, a Bootis, and Sirius, the remainder 

 give P = o"*o86, or if all stars of the first magnitude are 

 omitted, P = o"*o83. Again, if all stars with extreme 

 motions are neglected, and a value of P derived from the 

 nine stars which remain, with proper motions less than 2" 

 annually, it is found to be o"*o84. Prof. Gylden con- 

 siders that the near agreement of values obtained from 

 these two calculations, in which the extreme case of 

 brightness and motion enter, affords some support to the 

 inference that the relation indicated by the above formula 

 between parallax, apparent motion, and apparent bright- 

 ness may be taken as an approximation to the truth. It 

 may be remarked that Prof Peters found for the mean 

 parallax of a first-magnitude star, o"*i02 ± o"*o26; the 

 new value is within the limit of his probable error. 



