468 Mr. J. P. Gassiot on a Ruhmkorflf's Induction Apparatus. 



discharge in air will disappear, for there will then not be suffi- 

 cient time between the make and break contact to magnetize the 

 ii'on core, on which the intensity of the induced discharge mainly 

 depends. 



This form of the apparatus also enables the experimentalist to 

 examine the character of the single discharge, and which, in 

 respect to the phfenomena of stratification, corroborates the re- 

 sults I have previously obtained and communicated to the Royal 

 Society. 



On examining the single discharge, as taken from Ritchie's 

 coil by means of Mr. Wheatstone's revolving mirror, I found 

 the direct spark was elongated but not divided : if a Leyden jar 

 is introduced in the manner first suggested by Mr. Grove, the 

 length of the spark is much reduced, but is increased in bril- 

 liancy, becoming intensely bright and dense. When this dis- 

 charge is examined by Mr. Wheatstone's apparatus, it is instantly 

 resolved into two distinct sparks, not elongated as in the direct 

 discharge, but separated clear and defined. In my recent 

 communication to the Royal Society, I have shown that when a 

 Leyden jar is attached to the inner and outer terminal of the 

 induction coil, excited by a single cell of the nitric acid battery, 

 stratifications are observable in the dark portion of the discharge 

 when taken through a vacuum tube, such stratifications being 

 concave in opposite directions to those which emanate from the 

 positive terminal of the coil. The division of the spark by Mr. 

 Wheatstone's apparatus shows the cause of this appearance to 

 be due to the double discharge. 



The method adopted by Mr. Ritchie for the winding the wire 

 on his secondary coils (first, I believe, suggested by Poggendorff ), 

 is the same as used by seamen in coiling ropes on the deck of a 

 vessel : commencing with the inner circle, the coil gradually 

 extends to the outer circumference, the next layer is continued 

 from the outer to the inner, and this is repeated until the reel 

 is completed. This method secures the secondary coil fi'om 

 the risk of disruption ; but it becomes liable for the discharge 

 to pass from the internal terminal of the secondary to the pri- 

 mai-y, even when protected by a glass cover and thick gutta 

 percha. Mr. Ritchie has sent me a piece of a glass cover which 

 was thus fractured ; and having already starred, although not 

 actually perforated, one of my glass covers, I have not incurred 

 the risk of using the apparatus to its highest power. 



The maximum effect that could be attained with this apparatus 

 would, I conclude, be about 15 inches, the total length of the 

 three secondary helices. With five cells of the nitric acid 

 battery, each platina plate 4x8 inches, I obtained 10 inches 

 spark from two coils, a)id 5 inches from one. In one instance, 



