yune 9, 1881] 



NATURE 



131 



ductor. For the other experiments it makes little difference 

 whether the electrification of the point be positive or 

 negative, except that when the point is positively electrified 

 the illuminated surface is a little larger than when nega- 

 tively electrified. A larger disk of light can also be ob- 

 tained by working the machine at a greater velocity, but 

 at the same time the shadows are rather smaller. 



Prof. Holtz has also obtained the inverse phenomenon 

 of luminous-figures by two different means. If two 

 pointed needles are fixed horizontally side by side upon 

 the discharging rod opposite to the disk, there appears a 

 vertical streak of light across the glimmering field. If 

 the needles be replaced by a horizontal strip of metal with 

 its edge directed toward the disk, a vertical bright streak 

 is also produced. A short metallic tube affixed to the 

 discharging rod produces on the disk a dark central spot 

 surrounded by a nebulous bright ring. The second kind 

 of luminous-figures is produced in the manner shown in 

 Fig. 2, where a circular disk of metal or cardboard having 

 a central aperture of recognisable form is interposed 

 between the point and the screen. The result is a luminous 

 image of the aperture which, though well-defined at the 

 middle, is marred at the outer regions, the shadowed 

 portions appearing to encroach more upon the illuminated 

 parts as we pass to the peripheral region. The following 

 experiment is curious : — If a square aperture be chosen, 

 the luminous figure projectjd on to the silken surface 

 shows well-defined corners ; but if a small round disk of 

 card be interposed between the discharging point and the 

 square aperture the luminous square on the silken screen 

 at once exhibits rounded corners. 



Another interesting point connected with the shadow- 

 figures is that they can be fixed in a temporary manner, 

 like Lichtenberg's figures, by sifting upon the silken sur- 

 face lycopodium-powdcr or other fine dust. This collects 

 chiefly upon the contours of the figures, though under 

 certain conditions the luminous and shadowed parts ex- 

 hibit a contrasted density in the deposit of dust upon 

 them. These dust-figures have an obvious relation with 

 those obtained by Wiedemann from the discharge of 

 Leyden jars through a pointed conductor against the sur- 

 face of various bodies. It would be interesting to ascer- 

 tain whether by this process also shadow-figures can be 

 produced. 



In explanation of these appearances Prof Holtz pro- 

 pounds the view that they are due to a rectilinear dis- 

 charge of electrified particles from the point of the 

 discharging-rod, the discharge taking the general form of 

 a cone, but in which the paths of the outermost particles 

 diverge more widely as they approach the silken disk. 

 The function of the silk he believes to be to retard the 

 discharge, and thereby to increase the electric density 

 on the point. The conducting bodies which are interposed 

 in order to produce shadows act therefore by deflecting 

 the flying particles from their path, either by absorbing or 

 reflecting them. In many cases this action would appear 

 to be a repuhion, since the shadows are always larger than 

 the objects, and suffer more distortion by enlargement 

 nearer the borders of the disk. To explain the produc- 

 tion of the double shadows, the rather doubtful hypothesis 

 is advanced that there is a rectilinear discharge of particles 

 in both directions at once. 



Quite independently of these observations, the same 

 kind of phenomena have been investigated in America by 

 Messrs. Fine and Magie of the Green School of Science, 

 Princetown, N.J. These experimenters were aware of 

 the existence of shadows on the positive discharging 

 knob, but believed that they were the first to discover the 

 existence of a negative shadow. They found however 

 that non-conductors cast the best shadows, and added 

 the interesting observation that the lines of electrical 

 action were deflected by the presence of a conducting 

 body at the side of the field, and the form of the shadow 

 correspondingly altered. Negative shadows were also 



observed, they remark, some years ago by Prof. C. A. 

 Young. 



These shadow-figures become doubly interesting when 

 compared with the "molecular-shadows" obtained by 

 Crookes from electric discharges in high vacua Further 

 experiments are probably needed before their precise 

 nature is fully known. S. P. T. 



A 



BEN NEVIS OBSERVATORY. 

 PROPOS.^L was made a year or two ago to erect 

 an observatory on the top of Ben Nevis for meteoro- 

 logical observations, but nothing was done owing to the 

 want of the necessary funds. A committee has been 

 formed, however, within the last few months for the 

 purpose of raising a testimonial to Mr. David Hut'hison, 

 who did so much in opening up the West Highlands to 

 tourists with his steamboats, and we observe that it is 

 proposed that the testimonial take the shape of an 

 observatory on the top of Ben Nevis. The committee 

 is a large and influential one, and the proposed scheme 

 has every appearance of being successfully carried out. 



In the meantime the Scottish Meteorological Society 

 has commenced daily observations on Ben Nevis, which 

 will be continued during the summer months — the Society 

 having accepted a handsome offer by Mr. C. L. Wragge, 

 who has had experience of such work, to climb to the top 

 of Ben Nevis every morning in time to make observations 

 there at 9 a.m. A complete set of the best instruments 

 has been procured. The barometer (a Fortin), is an 

 excellent instrument, and is constructed to read as low 

 as 23000 inches, in the procuring of which Mr. Scott of 

 the Meteorological Office kindly gave his assistance. On 

 Tuesday, May 31, Mr. Wragge, with Mr. Livingstone, of 

 the Public Schools, and nine workmen ascended the 

 mountain, and the instruments were fixed and secured in 

 proper positions, and all, including the barometer, were 

 found to be in good working order. The regular observa- 

 tions began on the following day, June I, Mr. Wragge 

 being at his post on the top of the I5en, 4406 feet above 

 the sea, at 9 a.m. He remains an hour at the top, and 

 makes three observations, viz. at 9, 9.30, and 10 a.m. 

 Even during the stormy weather of Saturday last, the 

 observations were made and the observer back to Fort 

 William at 1.30 p.m., on which occasion the temperature 

 at the top was as low as 28°o. 



Simultaneously with the Ben Nevis observations, a 

 complete series of observations are also made near sea- 

 level by Mrs. Wragge. These observations, together with 

 the observations made at the neighbouring stations of 

 Roy Bridge, Corran, Landale, Airds, Lismore, and Dalnas- 

 pidal (1450 feet above the sea), will give the data required 

 in dealing with some of the more important problems in 

 meteorology. 



NOTES 

 Amongst the few existing institutions for the higher educa- 

 tion of women, perhaps none has done better work during the 

 last thirty years in a quiet, unobtrusive fashion than Bedford 

 College, York Place. The recent action of London University 

 in opeiiinsj its degrees to women has given a fresh impetus to 

 women' .s education ; and Bedford College has set itself the task 

 of providing the training for which London Univers ty offer.s 

 only the test — a task in which it has already achieved such 

 success as to give a sure promise of a brilliant future. The 

 fundi, however, at its di-posal, derived mainly from the bequest 

 of the late Mr-. Reid, prove inadequate to the strain thus put on 

 its resource.'!, and an appeal for support is now being circulated 

 which deserves the attention of the friends of education. In 

 that appeal details of the work and aim of ihe College will be 

 found. Space will only allow us to add that subscriptions will 



