per cent., and left a white crystalline substance, soluble in water, alcohol, and ether. The authors are at present engaged in the investigation of this product.

3d, The oxalate is obtained by treating the iodide with oxalate of silver. It crystallises, with one molecule of water, in clear hygroscopic plates.

Analysis gave the following results:

On carefully heating the salt to 110° C., the water of crystallisation is given off. At 146° C. the anhydrous salt decomposes into sulphide of methyl and pure oxalate of methyl

[(CH3)3S]2C2O4 = 2(CH3)2S+ (CH3)2C2O4

The chromate and the iodate of trimethyl-sulphine were also prepared. Heated to about 140° C. they both fuse, and almost immediately explode.

5. Extracts from two Letters by Professor Quincke on the Refractive Indexes of Glass and Quartz, as tested by Reflection from the Surface. Communicated by Sir William Thomson.

In answer to your question about the alteration of surface in quartz crystals, I place the glass or quartz plate whose refractive index X is to be determined between two right-angled flintglass prisms, with oil of cassia, and measure the angle 0, at which total reflection begins from the hypothenuse of the first flint-glass prism; the angle can easily be calculated from i, u the refractive index of the flintglass, and P the angle of the prism. Sunlight

1.

2.

falls from a collimator with a slit upon the

system of flint-glass prisms, and after passing

through the second prism is examined by a direct vision set of

prisms, I turn the system of flint-glass prisms until the spectrum appears to be broken off at a definite Fraunhofer line, measure the angle i, and thus obtain

Of course one can use flint-glass prisms other than right-angled ones, and, in fact, for measures of quartz, I have had flint-glass prisms made by Steinheil in Munich, in which i was only a few degrees. In a plate of quartz cut perpendicularly to the optic axis, one can easily determine in this way the refractive indices of the ordinary and extraordinary ray by interposing in front of the eye a Nichol's prism in the proper position. In fresh quartz plates I obtained almost exactly the same values as Rudberg:

1.54108 1.54207 1.54412 1.54710 1.54966 1.55365
1.54987 1.55065 1.55338 1.55622 1.55892 1.57166

1.54789 1.54933 1.55199 1.55508 1.55758 1.56192

The differences of the individual measurements in different specimens I attribute to difference in the properties of the specimens of quartz themselves.

In old quartz surfaces which have already been about twenty years in my possession, and in others which I have found in the

physical collections in Wurtzburg and Heidelberg, the refractive index for the Fraunhofer line D varied between 1.5141 and 1.5374 for the ordinary ray, and between 1.5216 and 1.5470 for the extraordinary.

I allow the first surface of the quartz to adhere by capillary attraction, and my large horizontal circle, by which μ and i are measured, reads to two seconds.

Crown glass plates from Steinheil, which had lain ten or twelve years in a press, and whose refractive index for D was 1·5245, gave, by total reflection at the surface, the refractive index 1.4903.

The alteration of the surface appears to me to be due, in quartz as in glass, to a chemical change of surface, perhaps to the vapour in the air forming a hydrate of silicic acid, or a hydrate of silic.

The above measures and arrangements have not yet been published, but they are entirely at your service if you can use them in your article on Elasticity.

I hoped to have sent you with the former ones some measures of the refractive indices of natural quartz surfaces, but then the observations have to be made with reflected light, which impairs their accuracy; besides, in spite of great trouble, I have not been able to procure any quartz whose surfaces were flat enough and complete enough for this inquiry. The only crystalline surface which I could examine seemed to have the same refractive indices as fresh polished surfaces. Besides, I am not astonished to find different refractive indices in different quartz crystals, since I have invariably found slight variations in the optical constants even for light transmitted through different specimens of crystals, for instance, in the amount of rotation of the plane of polarisation. Even if one had kept the crystal for thousands of years under the same physical conditions, for instance, at the same temperature, &c., still, according to my opinion, the mode in which it was originally formed would affect its final stationary condition. Crystals, like human beings, and like films of liquid upon heterogeneous solid or liquid surfaces, carry with them during their whole existence the mark of their origin or birth. Two bodies can only show properties extremely alike, never exactly the same.

PROFESSOR JENKIN called attention to experiments made by Mr Gott in St Pierre, and published in the Journal of the Society of Telegraph Engineers. Mr Gott converted two siphon recorders into a telephonic system by mechanically connecting the suspended coils with diaphragms. In this experiment the only conceivable mode of action was analogous to that suggested by Professor Graham Bell as the explanation of his telephone. This explanation, if not complete, was not, in Professor Jenkin's opinion, Professor Jenkin announced that he had, with Mr J. A. Ewing's assistance, constructed one of Mr Edison's phonographs, and that this instrument, like the telephone, gave a nasal intonation to the words spoken by it.

erroneous.

Monday, 4th March 1878.

D. MILNE HOME, LL.D., Vice-President, in the Chair.

The following Communications were read:

1. Proposed Theory of the Progressive Movement of Barometric Depressions or Storms; being in continuation of the Paper read before the Society on July 5, 1875. By Mr Robert Tennent.

In this paper it is not proposed to discuss in their relations to storms the effects of rain, of the earth's rotation, of areas of high and low pressure external to the storm-area, and of the prevailing westerly winds, which are doubtless occasional factors in the progressive movement of storms. What it is intended to show here is that storms possess in themselves a self-motive power, by which their onward movement over the earth's surface is determined.

It will tend to clearness if attention be pointed at the outset to two very different kinds of barometric depressions. The one which accompanies the true cyclones of the tropics is, on comparison with the height of the disturbance, of very limited extent, while

the other, of which our European storms are examples, and which alone are dealt with in this paper, is of very great extent as compared with the height. The modes in which these two distinct kinds of barometric depressions tend to fill up are widely different from each other, owing particularly to the degree in which the element of friction is introduced by the forces set in motion within the storm itself.

Mode in which a Barometrical Depression of a Narrow Diameter fills up. In this case, since the diameter of the depression is small as compared with the vertical height of the storm, it follows that the inflow of the air-currents towards the area of lower pressure will take place over a surface of comparatively small extent, and will consequently meet with but little retardation from friction. Hence the process of inflow toward the centre of the barometrical depression will take place with comparative facility in true tropical cyclones of small extent, and be therefore characterised by steep barometrical gradients.

Let A B C (fig. 1) represent a vertical section of such a depression, and let the small arrows a, b, c, show the direction in which it will tend to fill up over a surface of comparatively small extent, accompanied by a steepening of the gradients B A and B C.

Mode in which a Barometrical Depression of Wide Diameter fills up and in the process tends to open out.-In European and American storms, the barometer at their centres falls about as low as in tropical cyclones, but the barometric gradients are much less steep, and the disturbances cover a much more extensive region. Redfield has pointed out that their vertical height is often not more than the twohundredth part of their horizontal breadth. It follows from this essential difference between these storms and true cyclones that the mode of inflow of the air-currents towards the central low pressure can neither take place in the same manner nor with a