Dec. 1 8, 1879] 



NATURE 



159 



glass shade is also employed for steadying the light, by 

 keeping off convection currents. There seems to be an 

 objection to this form of lamp for accurate scientific 

 work, where it may be necessary to use an image of the 

 source of illumination. For instance, in certain spec- 

 troscopic comparisons of different lights only a small 

 portion of the image of the incandescent platinum would 

 fall upon the slit. Now the first difficulty that would be 

 met with would be as to the part of the platinum that 

 would emit a standard light. Near the contacts the heat 

 would be conducted away so rapidly that the colour of 

 the light would be of a different tint. 



Again, presumably near the middle of the limbs of the 

 U-shaped foil the temperature would be slightly higher 

 than at the outsides ; in fact, no two portions of the foil 

 would be exactly at the same temperature. 



For work, then, of this class, the standard seems to 

 fail in an important particular. 



The writer of this notice made many experiments on 

 this point some years ago, and it was this objection that 

 led him to abandon the idea of a platinum standard light 

 of a form somewhat similar to that of Mr. Schwendler. 



For a standard perfectly suited to scientific work, per- 

 haps the following definition will be found tolerably 

 exact : — It should be a body (solid or liquid), some known 

 area of the surface of which can be kept at a high con- 

 stant temperature. It seems probable that a combination 

 of a body of good with one of a bad conductivity will 

 eventually be found to offer suitable materials for a really 

 trustworthy standard. 



It would be unjust to conclude this notice without 

 paying a testimony to the great value of the experiments 

 which have been carried out by Mr. Schwendler in this 

 research. It is quite possible that a modification of his 

 platinum standard may be constructed which will elimi- 

 nate the defects which are to be found in it. It is 

 certainly a step in advance of the gas or candle standard 

 for everything beyond merely technical work, but it is not 

 of the same accuracy as other scientific units. W. A. 



FLOW OF VISCOUS MATERIALS— A MODEL 



GLACIER 

 '"PHREE or four years ago an experiment was arranged 

 -*• by Mr. D. Macfarlane and myself for the purpose of 

 •showing the flow of a viscous mass and for illustrating 

 glacier motion. The experiment then commenced gave 

 rise to others of a similar nature. These experiments 

 have proved so interesting that I venture to describe 

 some of them to the readers of Nature. 



Shortly after his discovery of the true nature of glacier 

 motion, the late Principal Forbes was much pleased when 

 one of his students, now the Rev. C. Watson, of Largs, 

 •showed him a quantity of shoemakers' wax which had 

 been gradually flowing down on the bottom of a vessel 

 accidentally left on an incline. Forbes was delighted 

 with the wax, and considered it an admirable illustration 

 of viscous flow. This was told to me in conversation 

 some four years ago, and it occurred to me that a pretty 

 illustrative glacier might be made with shoemakers' wax, 

 and we proceeded to construct it. The model glacier has 

 been shown year after year to the natural philosophy 

 ■class in Glasgow, and has proved interesting and instruc- 

 tive beyond expectation. 



A little wooden ravine was constructed, with a number 

 of steep declivities and precipices and some more gentle 

 slopes. There is one place, also, where the ravine is 

 narrowed by projections inwards, which nearly meet each 

 other. At the upper end of the ravine there is a flat part, 

 on which ordinary shoemakers' wax is piled — as where snow 

 collects at theupperend of the natural ravine ; and from this 

 •collecting-ground the material flows down steadily through 

 the ravine, giving on a small scale a most perfect display 

 of the flow of a semi-solid material. At the beginning of 



each winter session a supply of shoemakers' wax is given 

 at the top, and during the session the flow goes on slowly 

 and steadily; hardly perceptible from day to day, but 

 progressing from week to week, and from month to 

 month. Every one knows what a brittle substance shoe- 

 makers' wax is at ordinary temperatures. A lump of it 

 allowed to fall on the ground flies into a thousand pieces. 

 Watching this brittle apparent solid flowing down an 

 inclined plane, brings very vividly before the mind the 

 real nature of the glacier' s flow. To imitate on the small 

 scale Forbes' s celebrated experiment of planting a row of 

 stakes in the glacier, in order to compare the flow in the 

 middle with the flow at the edges — the experiment which 

 really established the fact of viscous flow — I have some- 

 times put a row of dots of white paint across our pitchy 

 glacier. In a few days the more rapid motion of the 

 middle portion, and the less rapid motion of the parts 

 near the edges, is made apparent. There are others of 

 the glacier phenomena which are also beautifully imitated 

 by the shoemakers' wax. Little crevasses are sometimes 

 formed, though not very often owing to the great effect 

 of temperature on the plasticity of the material ; and the 

 cross-markings that are noticeable at the foot of a 

 glacier are brought out extremely well. 



Last year Sir William Thomson commenced a new and 

 curious experiment on shoemakers' wax as a viscous 

 material. A large circular cake of it about eighteen 

 inches across and three inches thick was made. This was 

 put into a shallow cylindrical glass vessel, which was 

 filled with water to keep the temperature from varying 

 with any great degree of rapidity. Below the cake a 

 number of corks were put, and on the top there were put 

 some lead bullets. The result has been that in a year the 

 corks have floated up through the wax, and are coming 

 out at the top ; the bullets have sunk down through the 

 wax, and have come out at the bottom ; and this, it is to 

 be observed, has gone on while the wax was at all times 

 in such a condition as to be excessively brittle to any force 

 suddenly applied, such as a blow from a hammer, or such 

 as would be occasioned were the cake of wax to be allowed 

 to fall on a stone floor. J. T. Bottom ley 



THE SCOTTISH ZOOLOGICAL STATION 



SOME months ago the opening of a zoological station 

 on the Scottish coast was mentioned in these pages. 



This station — the first enterprise of the sort in Britain — 

 has been established in connection with the University of 

 Aberdeen, and under the directorship of the Professor of 

 Natural History, Dr. Ewart, who was, this year, assisted 

 in the conduct of the station by Mr. Patrick Geddes. 



The site chosen was the little fishing station of Cowie, 

 about half a mile north of Stonehaven, and fifteen miles 

 south of Aberdeen. But one of the chief advantages of 

 the station is that it is not a fixed building of brick or 

 stone, but a movable one of wood, which can be taken, if 

 necessary, to a new place every year, and, after the 

 season's work, taken down and packed up for the winter. 



The annexed cuts give an excellent notion of the 

 appearance and internal arrangements of the place. It is 

 a wooden structure (Fig. 1) about 32 feet long by 16 wide, 

 supported on low wooden piers and having a thin wooden 

 roof covered over with sailcloth. In each of the longer 

 sides are five windows, in one of the shorter sides the 

 door, in the other two windows. Inside (Fig. 2), a parti- 

 tion divides the building into two parts— a larger, the 

 laboratory proper, with eight out of the ten side windows, 

 and a smaller, the library and director's room, with two 

 of the side and both end windows. 



In the library there is a bench or working-table (Fig. 2, 

 T) running round three sides, with shelves (5) above, for 

 books, apparatus, and bottles. In the laboratory there is 

 a table (7") to each window, intended to accommodate two 



