236 Intelligence and Miscellaneous Articles. 



grows continuously. But in our case the duration of the spark is 

 about equal to the tenth part of the whole period of an oscillation, 

 and therefore by no means inconsiderable *. Its average length is 

 determined by comparing the time between the stroke of the pendulum 

 which breaks the primary conduction and the first zero-point of the cur- 

 rent, with the time between the successive zero-points. The former 

 is longer, because, besides the period of half an oscillation, it com- 

 prises also the duration of the spark; and the amount of this can be 

 approximately found by means of such a comparison. 



On the other hand, the successive zero-points of the current can 

 be very sharply determined, even with the more distant position of 

 the secondary spiral. As, even with such feeble electromotive 

 forces and spirals of so few turns as I used in the primary circuit, 

 the duration of the spark is never constant (the reason of which is 

 probably to be sought in the throwing-off of platinum particles by the 

 sparks), the deflections about the division-mark corresponding to 

 zero are, even with a good arrangement of the apparatus, sometimes 

 positive, sometimes negative ; on the contrary, at the preceding and 

 succeeding divisions they are either exclusively or preponderantly in 

 one definite direction. 



With the arrangement described, at which I had arrived after 

 many trials, it was shown that the greater distance of the tiuo spirals 

 (136 centims.) did not alter the situation of the zero-point of the induced 

 current by one division of the micrometer — that is to say, by -j^^j ytj °f 

 a second. If, then, the inducing effects are actually propagated with a 

 definable velocity, this must be greater than 314,400 metres, or about 

 42' '4 geographical miles [about 195 British statute miles] in a second. 



I have hit upon preparations for a further refinement of these 

 measurements. How far this can be carried, will, it appears to me, 

 depend chiefly on how far the spark at the place of interruption can 

 be reduced when a very small resistance and very small electromotive 

 force are given to the primary circuit, and when the turns of wire 

 forming it are removed as far as possible from one another. — Mo- 

 natsber. d. Kon. Preuss. Akad. Berlin, May 1871, pp. 292-298. 



ON A NATIVE SULPHIDE OF ANTIMONY FROM NEW ZEALAND. BY 

 M. M. PATTISON MU1R, F.C.S., STUDENT IN THE LABORATORY 

 OF THE ANDERSONIAN UNIVERSITY, GLASGOW*}". 



In the gold mines at the Thames (New Zealand) there are found 

 tolerably large quantities of grey antimony ore or stibnite, associated 

 with the quartz and other rocks of the older series from which gold 

 is extracted. The analysis of a sample of this stibnite, which I ob- 

 tained about a year ago, I have now the honour to lay before the 

 Association. 



* The relatively slow decrease of intensity of the primary current during 

 the spark is also evidently the reason that, as I previously found, in an in- 

 duced spiral with more than 7000 electric oscillations in a second the latter 

 turned out so feeble : the interruption is then not sufficiently sudden for 

 the brief duration of the oscillation. 



t Communicated by Prof. T. E. Thorpe, having been read at the Meet- 

 ing of the British Association held at Edinburgh, August 1871. 



