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Proceedings of the Royal Society of Edinburgh. [Sess. 
glass tubes. Brass terminals and so on were heavily coated with sealing- 
wax ; the battery of Leyden jars stood on a thick glass base-board, which 
in turn stood on ebonite pegs. 
The main object of the investigation, as already mentioned, was to give 
an explanation of the Lullin experiment. It will at once be obvious that 
such would have a special interest for makers of large induction coils, who 
often experience strange and unaccountable trouble with their insulations, 
perforations occurring between the coils.* It would, however, be out of 
place here to enter on the results of these experiments : we desire only to 
m ic8orie.Teft 
mention a few phenomena, met with as the experiments proceeded, which 
bear on that described by Dr Turner. 
I. Dr Turner says : “ The introduction of a dielectric between the poles 
will greatly facilitate the sparking, provided the dielectric be placed near or 
against the positive pole.” The statement is somewhat loose, ignoring, as it 
does, the questions of dielectric thickness and superficial area (if both be 
great enough, sparking will certainly not be facilitated) and the question of 
whether the spark passes by perforation of the dielectric or round about its 
edge. It is certainly the case, however, that within certain limits for the 
dimensions of the dielectric, sparking may often be induced by placing it 
“ near or against the positive pole ” ; and the opposite effect may be obtained 
* Kiessling and Walter, Annalen d. Physik (4), Bd. xi., 1903, p. 586. 
