410 Intelligence and Miscellaneous Articles, 



that of A. Jurensis, or all those resting on the zone of A. spinatus 

 and superposed by that of A. Murchisonite, — the beds formerly- 

 termed ' the Sands of the Inferior Oolite ' being referred to the 

 Upper Lias. The sections exposed at Black Venn, Westhay Cliff, 

 Golden Cap, and Down Cliffs were described in succession, the 

 fossils found in each bed being given, as well as the vertical range 

 of the Ammonites. 



The occurrence of a new genus of Belemnitida in the Belemnite- 

 beds of the Middle Lias was noticed, and a description of its general 

 features given, with a list of the associated fossils. 



Mr. Day then exhibited, in the form of a generalized section, the 

 different Ammonite-zones into which the Middle and Upper Lias of 

 the Dorsetshire coast could be divided, and gave lists of the fossils 

 peculiar to each. 



LV. Intelligence and Miscellaneous Articles. 



ON A METHOD OF VARYING THE TENSION OF THE DISCHARGE 

 OF AN ELECTRIC BATTERY, AND OF A RTJHMKORFF's COIL. 

 BY M. A. CAZIN. 



TT is known that the elements of a battery may be associated in two 

 * ways, according to the nature of the effects which it is desired to 

 produce. 1 have thought that analogous arrangements might be used 

 with condensers of statical electricity. Hitherto the discharge of 

 Leyden jars has only been used by uniting the armalures of the same 

 name, so as to increase the quantity, and association in series has 

 only been used to charge several batteries at once. J am not aware 

 that any one has observed the properties of the spark obtained in 

 discharging the series by its extreme coatings, although the analogy 

 of a series of condensers with the pile has long been remarked. Thus 

 the illustrious Biot in his Traite de Physique describes experiments 

 in which he has measured, by means of a proof plane, the tension on 

 the different plates of an insulated series ; and he points out the in- 

 crease of the tension from the middle to the extremities of the series, 

 although it cannot be concluded from his observations that the length 

 of the spark obtained by these means is much larger than with a 

 single condenser : this is what I have had occasion to observe. 



The first experiments were made by M. Ruhmkorff with the aid 

 of his powerful induction-coil. He himself arranged everything 

 with his known ability, and with a disinterestedness which I here 

 desire to thank publicly. The poles of the coil being connected on 

 the one hand with the extreme armatures of a series of insulated 

 Leyden jars, and on the other hand with a discharge as in the ar- 

 rangement adopted for a single condenser, the length of the spark 

 which passes between the arms of the discharger increases as 

 the number of jars increases, while its magnitude, its lustre, and the 

 report which accompanies it scarcely appear to diminish. Without 

 condenser the spark of the induced discharge was from 300 to 360 



