March 8, 1894] 



NA TURE 



433 



<ation of his book, namely, in the first report to the British 

 Asfociation on electrical standards (see report of the Newcastle 

 meeting of the Association in 1863, p. 160) called attention, in a 

 "Note on the Table of Dimensions," to the provisional 

 character of the electrostatic and eleclromagnetic series recom- 

 mended by the committee, and since widely adopted. 



He there points out that "if we take into account the co- 

 efficient of magnetic induction of the medium in which we 

 woik," this quantity, /t, will enter into the dimensional equa- 

 tions ; and he gives an illustration of this under a particular 

 hypothesis. The whole note is worthy of very careful attention. 



This pregnant note, so far as my memory serves me, was 

 emitted frcm the reprint, by Prof. Fleeming Jenkin, of the 

 British Association reports on electrical standards, and may 

 now be easily overlooked. It seems, therefore, well to call 

 attention to it. G. Johnstone Stoney. 



8 Upper Hornsey Rise, N., February 26. 



Experiments in Elementary Physics. 



I NOTICE on p. 379 a description of a new form of Boyle's 

 tube used by Dr. J. Joly. The following, which I have now 

 used for about six or seven years, I have found very convenient 

 for school use, where it is a disadvantage to have much pouring 

 to or fro of mercury. 



A piece of Sprengel tube about I m. long is fastened along 

 a metre scale, one end having been previously closed. The 

 metre scale is then mounted so as to be capable of rotating 

 about a horizontal axis, and a thread of mercury about 30 cm. 

 long is introduced into the tube so as to leave an air space 20 to 

 30 cm. long at the closed end. The volume of air is read off 

 along the scale, and the pressure varied by rotating the tube 

 about its axis, and measuring the vertical height of the mercury 

 column. By this means pressures greater or less than one 

 atmosphere can be easily obtained, and the product v. p. shown 

 to be constant with considerable accuracy if ordinary pre- 

 cautions are taken. 



To show that when the volume is constant the pressure of a 

 gas varies with the absolute temperature, I use a vertical tube 

 about 40 cms. long, surrounded in the upper part by a water 

 jacket. The upper end is closed, and the lower connected by 

 stout rubber tubing to a long tube fixed to a wooden arm — the 

 end of this arm nearest to the vertical tube being hinged to the 

 base board. The two tubes are filled with mercury, so that it 

 rises to a certain mark on the vertical tube, and nearly fills the 

 long tube when the surfaces are about the same level. The air 

 in the vertical tube is heated by passing steam into the water in 

 the jacket, and when the desired temperature is reached, the 

 wooden arm with its tube is raised till the air resumes its former 

 volume. The pressure is then the height of barometer + diff. 

 in height of the two mercury surfaces. 



A method of illustrating magnetic lines of force, which I have 

 found useful, is to thrust a magnetised knitting-needle through a 

 cork so that it can float vertically in a large vessel of water. If 

 now a magnet is supported just above the water surface, the 

 needle moves along a line ot force. The lines due to two or 

 more magnets may easily be traced out on this plan. 



Blairlodge School, Stirlingshire. W. Rheam, 



Spectacles for Double Vision, 



Many years ago, on recovering consciousness twelve hours 

 after a railway accident in which my jaw was broken, I saw 

 everything double in this position : — 



The image seen by one eye was lifted above that seen by the 

 other to the extent of about one-eighth the distance of the object, 

 and was shifted a little to one side, while the two images were 

 inclined to each other at an angle of about twelve degrees. This 

 double vision still continues. It produced little inconvenience 

 until I had to use spectacles for reading and writing ; but the 

 forcible bringing of the two images together then injured one eye 



NO. I 27 I, VOL. 49] 



so much that it soon became ot little use. I found that to use 

 one eye alone was equally bad ; a white fog seemed to rise 

 before the one not in use, and it speedily became almost blind. 

 A five weeks' sea voyage, where I had nothing to read, improved 

 the weak eye wonderfully. After consulting some of the best 

 oculists and opticians, I got a pair of spectacles made with 

 prismatic lenses, which brought the centres of the two images 

 together, but left them still inclined at the same angle. Rotating 

 these lenses simply shifts the images parallel to themselves. 

 After two years' use the spectacles had produced a beneficial 

 effect ; but the improvement stopped half-way — like the half- 

 remedy. 



Fortunately, I met Mr. C. Vernon Boys, F. R. S., of South 

 Kensington, explained my difficulty, and he at once pointed out 

 the remedy, as follows : — A pair of right-angled prisms are 

 placed in the form of a rhombus, and a small distance apart. 

 When one is turned relatively to the other about the common 

 visual axis, the image is turned through double the angle. When 

 one is turned relatively to the other about a direction perpendi- 

 cular to that axis in a horizontal plane, if the greater face of the 

 prism is horizontal the image is raised or lowered. If the two 

 prisms are turned together about the common visual axis, the 

 image is shifted to the right or left. The images seen by the 

 two eyes can thus be made to coincide exactly in every respect. 



I have had a pair of prisms mounted in this fashion on 

 common spectacles in front of the stronger eye. The prisms 

 have facets only seven-sixteenths of an inch square ; they 

 are very light, and although small, yet give a sufficient field of 

 view. There being now absolutely no strain on the weak eye 

 in reading or writing, I have no doubt an improvement will soon 

 set in. 



I think this information should be disseminated among ocu- 

 lists and opticians, as the contrivance might be useful to others 

 similarly afflicted. T. I. Dewar. 



Recent Local Rising of Land in the North-west of 

 Europe. 



During January of 1894 the local papers of Sweden, Nor- 

 way, and Finland reported the occurrence of underground 

 shocks or tremblings of the ground, accompanied with noises. 

 The zone seems to be east and west on about 60^ of latitude, 

 from about Drammen in Norway across Sweden to Hango on 

 the southern part of Finland. 



In Norway shocks were felt at the beginning of this year in 

 several places. On the night of January 2, tremblings of the 

 ground were felt at Navnaa, in Grue (lat. 60° 28'), and at 

 several places in Solor, throughout the whole night and also on 

 the following night. Loose things in the houses were much 

 shaken, and an examination of the earth surface showed cracks 

 about 2 cm. wide in several places. 



On the night of January 3, three strong shocks were felt at 

 Lower Eker in Mjondalen (lat. 59° 38'). The last one shook 

 the houses and all loose things. 



In Sweden, on the night of January 3, a shock and under- 

 ground noise was heard at Hedemora (lat. 60° 20'), and lasted 

 two seconds. A shock was also felt at Mora in Dalarne (lat. 61°), 

 and a crack in the ground, 2 cm. wide and one kilometre long, 

 was found to have resulted from it. On January 24 a shock was 

 felt in Dalarne at Stora Tuna (lat. 60° 27'). It lasted only two 

 seconds. The same trembling was also felt at Uddnas (about 

 thirty English miles to the west from Tuna). 



An underground noise, not very strong, was heard at Fin- 

 spong (lat. 58^ 40'). It lasted one and a half minutes. 



A strong underground shock was felt on February i at Wil- 

 helmsberg in Asker (lat. 59° 35')- It appeared to pass from 

 north-west to south-east, and gave rise to a sound like thunder 

 in the Iron mine department, and was felt at a distance of two 

 miles from this place. 



In the town of Ekeniis (lat. 60°), in the south-west corner 

 of Finland, underground shocks were felt on the evening of 

 January 2, and repeated until 2 o'clock in the morning. The 

 shock was felt strongest in an open field to the west of the 

 town, where three cracks in the ground were visible ; one of 

 these rents had a length of 240 feet, and crossing this was 

 another running west, and of 400 feet length. Some people be- 

 lieved that the ground was raised. The following day two more 

 shocks were felt, but they were not so strong as the preceding 

 ones. 



Stockholm, February l8. 



C. A. LiNDVALL. 



