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questions are raised concerning the latter :-(1) Can a succession be traced below the Purple Slates similar to that which the author has described as occurring in Caernarvonshire? and (2) Where is the most natural break in the series, and does it show an unconformity? With reference to the first question, the author gives his reasons for concluding that, as far as the succession is seen in the Harlech area, it is similar to that of Caernarvonshire. A group of Purple Slates is described which so closely resembles the Llanberis and Penrhyn Slates that he considered himself justified in definitely correlating them with those slates. Below these are slaty greywackes, which, if not identical with those of Caernarvonshire, bear a greater resemblance to them than any other part of the series does. No older beds are seen. Above the Purple Slates are the Harlech Grits proper.
In discussing the second question, the author describes conglomeratic beds occurring some distance above the base of these Harlech Grits; but at Pont Llyn-y-Crom the junction between them and the underlying Purple Slates shows features recalling what is seen at Bronllwyd. He discusses the possible existence of an unconformity at the base of these grits, and concludes that on the whole the phenomena point, though not very strongly, to an unconformity of no great importance.
The concluding part of the paper is occupied with a consideration of the question of classification of the Cambrian strata and those in juxtaposition with them.
XIII. Intelligence and Miscellaneous Articles.
ON THE VELOCITY OF SOUND IN GASES.
To the Editors of the Philosophical Magazine.
READ in No. 232, September 1894, of the Philosophical Magazine a paper by Mr. Webster Low, "On the Velocity of Sound in Air, Gases, and Vapours for Pure Notes of different Pitch." I deem it important to acquaint the Editors of the Philosophical Magazine that as long ago as 1881 I used a method nearly identical with Mr. Low's in order to determine the velocity of sound in some gases (air, CO,, N,O), and particularly in chlorine, its value for this gas being till that time quite unknown. My results were published in the Acts of the Venetian Institute*, and in abstract in other periodicals t. As to chlorine, which was
* Atti del R. Istituto Veneto di Scienze, Lettere ed Arti, serie 5, vol. viii. p. 494, and serie 7, vol. iv. p. 1113.
Journal de Physique théorique et appliquée, vol. x. p. 410 (1881); Beiblätter zu den Annalen der Physik und Chemie, vol. v. p. 564 (1881).
the gas that interested me the most, I found at 0°
Some months later Mr. Strocker found for chlorine with a method quite different from my own,
INFLUENCE OF MAGNETIC FIELDS ON THE ELECTRICAL
To the Editors of the Philosophical Magazine.
I regret that mention of the papers by Dr. Edm. van Aubel in the Annales de Chimie et de Physique for 1889, and in the Journal de Physique for 1893, was omitted from my paper "On the Influence of Magnetic Fields on the Electrical Conductivity of Bismuth" in your Magazine for November last. In his work on the Temperature-Coefficient of Bismuth, van Aubel found that it was considerably changed in a magnetic field; and at the "Congrès des Électriciens" in Paris in 1889 he emphasized the necessity for observing the temperature, in measuring magnetic fields by the resistance of bismuth spirals.
I remain, Gentlemen,
The Yorkshire College, Leeds.
JAMES B. HENDERSON.
ON THE INFLUENCE OF TEMPERATURE ON THE SPECIFIC HEAT OF ANILINE. BY E. H. GRIFFITHS, M.A.
NOTE, Dec. 7, 1894.—In a communication made to the Royal Society on November 22, Professor Schuster pointed out an error in my determination of the value of J, viz. that I had not made a necessary correction for the specific heat of the air displaced by the water; for the method I had adopted gave the difference in the rate of rise when a certain space was filled first with air and then with water. This correction raises my value of J by about 1 in 4000.
Now the specific gravity of aniline (1·02) but slightly exceeds that
of water; and as the method described in the preceding pages also depends upon the measurement of differences in the rate of rise, the correction would eliminate and would, therefore, not affect the values of the specific heat of aniline as given in Table VII. Again, if there are any errors in the values of the electrical standards upon which my determination of J depends, they also would eliminate during the calculations by which the specific heat of aniline was ascertained. There can, therefore, be no doubt that the value assumed for J (4·198 × 107) is the correct one to be used for the reduction of the observations on aniline.
ON THE DIELECTRIC POWER OF ICE. BY M. A. PEROT.
I published on June 29, 1894, the result of experiments made to determine the dielectric constant of ice by electrical oscillations. In calculating these experiments, which I had carried out as for glass, I made an error due to the external capacity, which in those experiments is altered, the condenser being wholly or partially immersed in the dielectric. M. Blondlot having pointed out the disagreement between his results and those which I had obtained, I have gone through the calculations, and made new experiments, the result of which is given below:
Mean √K=1·43; K=2·04.
-Comptes Rendus, October 8, 1894.
ON THE REFRACTION AND DISPERSION OF ELECTRICAL RAYS. BY E. GARBASSO AND E. ASCHKINASS.
The authors summarize the results of their research as follows:We have shown that the rays proceeding from a Hertz's primary conductor may, by means of a prism built up of resonators, be resolved into a spectrum, and draw from this the following conclusions::
(a) The rays of electrical force emitted are not necessarily to be regarded physically as monochromatic, but as compound, with as much justification as ordinary light.
(b) Helmholtz's theory of colour-dispersion acquires fresh support from our experiments.-Wiedemann's Annalen, No. 11, 1894.