_488 



NATURE 



[Sept. 14, 1882 



Report of the Committee on Electrical Standards. — Mr. Taylor 

 had been engaged during the past year in determining the effect 

 of the annealing of wires on the temperature co-efficient of their 

 resistance. The experiments were not yet concluded, but .so far 

 they had shown that the effect of annealing was enormous, in 

 some cases altering the temperature co-efficient by as much as 

 50 per cent The Committee hoped that Lord Rayleigh would 

 arrange a system for testing resistances at the Cavendish Labo- 

 ratory. In connection with this report Lord Rayleigh made some 

 remarks On making Standard Resistance Coils equal to Multiples 

 of an Original Unit Coil. The usual method is to make a copy 

 of the unit ceil ; by combining these, a coil of two units can be 

 made, then of four, five, and so on. Ky this means the errors 

 would accumulate. The method he proposed was simpler than 

 this. Three coils each of three units resistance, placed in 

 multiple arc, are equivalent to one unit, whilst in series the 

 resistance amounts to nine units. This, with the addition of the 

 original unit, makes a resistance often units. The observations 

 should be made quickly after one another, and he explained an 

 arrangement of mercury cups by which this was effected with 

 rapidity. 



Report of the Committee on Meteoric Dust, by Prof. Schuster. — 

 The report referred to the work of M. Tissandier, who has 

 found magnetic particles of iron in the dust gradually settling 

 down in dry weather, or precipitated by rain or snow. These 

 particles are of various shapes, but the most remarkable form is 

 a spherical one, which conveys the obvious information that the 

 particles at one time must have been in a state of fusion. These 

 have been found in the snows on the slopes of Mont Blanc, at a 

 height of nearly 90CO feet, in the sediment of rain collected at 

 the observatory of Sainte Marie du Mont, and in the dust col- 

 lected at different elevated positions. For an explanation of 

 these magnetic spherules we are reduced to three alternatives. 

 The particles may be of volcanic origin, they may have been 

 fused in our terrestrial fires, or they may be meteoric. All the 

 volcanic dust which the author has had at his disposal was care- 

 fully examined under the microscope, but its appearance was 

 found to be altogether different from the supposed meteoric dust. 

 Such also seems to be the conclusion arrived at by Tissandier. 

 No iron spherules to the author's knowledge have been found in 

 volcanic dust. The smoke issuing from the chimneys of our 

 manufacturing towns contains iron particles similar in appear- 

 ance to those to which Tissandier ascribes a meteoric origin. 

 That some of these particles are found very far from any terres- 

 trial sources which can produce them, would not perhaps tell 

 conclusively against their terrestrial origin, but chemical analysis 

 seems to settle the point. The iron particles issuing from our 

 chimneys contain neither nickel nor cobalt, while these metals 

 were found by Tissandier to exist in the microscopic magnetic 

 particles found in rain-water collected at the observatory of 

 Sainte Marie du Mont. We are, therefore, driven to ascribe 

 1 cosmic origin of these particles. During the last year the 

 author has examined microscopically small iron particles 

 from [the sand near the great pyramids, from the desert of 

 Rajpootana, and from the Nile mud near the village of 

 Sohag. The sand from the pyramids contains an appreciable 

 quantity of magnetic particles. The great part of these particles 

 are angular, and doubtless are due to the debris of magnetic 

 rocks ; but here and there spheres are found exactly like those 

 described by Tissandier, and about the same diameter, that is 

 o'2 to O'l mm, The Rajpootana sands are not yet completely 

 investigated, but as yet there has been no appearance of metallic 

 iron. The author then passes on to consider the debris left 

 behind in our atmosphere by the passage through it of shooting- 

 stars. Tissandier has examined the dust found on meteors, and 

 has found that it resembles in appearance the magnetic particles 

 found in other places. The question arises, how is it that the 

 red hot sparks from the meteors do not get oxidised, and the 

 author pointed out that at high elevations the proprotion of 

 oxygen in the atmosphere is very small, at a height of ico kilo- 

 metres being about 4 per cent, of the whole, supposing the tem- 

 perature the same throughout the atmosphere. He also drew 

 attention to the fact that a line in the spectrum of the aurora has 

 not been recognised as belonging to any known substance, and 

 from his experience in observing the spectra of oxygen and 

 nitrogen under very various conditions, he felt convinced that it 

 was not due to oxygen or nitrogen, but to some unknown gas of 

 very small density. He pointed out that at a great height the 

 density of this would only very slightly be diminished, and 

 although of extremely small density, would nevertheless form by 



far the largest part of the atmosphere there. Consequently the 

 meteoric sparks would only meet a very small proportion of 

 oxygen. He mentioned that the spherules might be easily pro- 

 duced artificially by moving a file over a copper wire conveying 

 a current of electricity. Collecting tire sparks which fly off, 

 these were found 10 contain a large proportion of spherules 

 similar to those referred to meteoric origin, together with angular 

 specimens such as had been found in some of the sands. 



In the Report of the Committee on Wind Pressure it was stated 

 that the maximum pressure on small plane surlaces had been 

 ascertained to exceed 80 lbs. and even 90 lbs. per square foot. 

 The pressure over any large area was still a matter of consider- 

 able uncertainty, but it was possible that the maximum pressure 

 of 56 lbs. allowed by the Board of Trade might take effect over 

 the whole of very exposed structures. The cases of wind and 

 water pressure were somewhat analogous, at any rate with regard 

 to the proper method of determining the relative exposure in 

 various positions. In the latter case this might be done by a 

 comparison of the readings of anenometers differently located. — 

 Prof. W. C. Unwin remarked that some form of pressure guage 

 of considerable delicacy was needed which could be applied to 

 all parts of a roof. Mr. Barlow said that the Board of Trade 

 rale was capable of being amended, and this no doubt would be 

 done as soon as further knowledge was forthcoming ; in the pro- 

 posed Forth Bridge 3000 tons of steel would be employed for 

 resisting wind pressure. 



In the Report of the Committee on Screw Cuages it was stated 

 that there is at present no universally recognised form of screw- 

 thread and no specified number of threads to the inch. For 

 telegraphic and electrical apparatus some coherent and uniform 

 system is much wanted. The report gave an account of the 

 efforts made in Switzerland towards this end, and explained the 

 screw guage finally adopted by that country. Much credit is 

 due to Sir Joseph Whitworth for his important work in connec- 

 tion with the improvement of the system in England. The 

 Committee asked to be re-appointed. 



SECTION A— Mathematical and Physical 

 Oh a Similarity between Magnetical and Meteorological Weather, 

 by Balfour Stewart, M.A., L.L.D., F.R.S., Professor of Physics 

 at the Owens College, Manchester. — It has been hitherto sup- 

 posed that there is no traceable likeness between the magnetical 

 and meteorological changes of the globe. The former have 

 been imagined 10 be of a cosmical nature affecting all parts of 

 the earth at the same moment of time, while the latter are well 

 known to be of a local and progressive nature. As a matter of 

 fact, all attempts to trace a likeness between simultaneous 

 magnetical and meteorological phenomena have been without 

 success. 



There is however one class of magnetical phenomena that 

 are of a progressive nature. I allude to the diurnal variations ol 

 the magnetic elements caused by the sun. Of these the solar- 

 diurnal variation of the magnetic declination — that is to say the 

 variation of the position of a freely suspended magnetic needle 

 is that which has been most observed aud best understood. 



It has been noticed that the diurnal progress of this vari linn 

 is not unlike that of atmospheric temperature ; the hourly turning 

 points in both being pretty nearly the same. Both phenomena 

 too are regulated by the local time at the place of observation, 

 and hence are of a progressive nature, travelling with the sun in 

 his apparent course from east to west. Both phenomena too 

 are subject to a well-marked annual fluctuation, the diurnal 

 temperature range, for instance, or the diflerence between the 

 indications of the maximum and the minimum thermometers being 

 greater in summer than in winter ; and in liUe manner the 

 diurnal declination range or the difference between the east and 

 the west positions of a suspended magnet being greater in 

 summer than in winter. Finally both phenomena appear to be 

 subject to the influence of something which may be called 

 weather. Sometimes we have very hot days and cold dry nights 

 in which the diurnal temperature range is very great, succeeded 

 by close rainy weather in which the diurnal temperature 

 oscillation is very small. In like manner we have sometimes a 

 very large and at other times a comparatively small diurnal 

 oscillation of the magnetic needle, so that it too is affected by 

 the influence of magnetic weather. The question which I now 

 wish to put is the following : Is there any connexion between 

 these two weathers ? between the temperature -range weather, 

 and between declination-range weather, both defined as above ? 



