1912-13.] New Method of Starting Mercury Vapour Apparatus. 117 
X. — A New Method of Starting Mercury Vapour Apparatus. 
By John S. Anderson, M.A., B.Sc., 1851 Exhibition Science 
Scholar (Glasgow) ; and George B. Burnside, Mechanical Assistant 
to the Professor of Natural Philosophy in the University of 
Glasgow. Communicated by Prof. A. Gray, F.R.S. (With One 
Plate.) 
(MS. received January 8, 1913. Read February 3, 1913.) 
The mercury vapour lamp,* although very economical in its use of electrical 
energy,*]* is not employed very extensively at the present day for illuminating 
purposes, chiefly because the light it emits is not white, but of a greenish 
hue. Many attempts have been made to produce the deficient red radia- 
tion, but these have so far not met with any great success.! The lamp, 
however, is useful as an illuminant where the colour of the light is of no 
great importance, such as in public works, etc. Further, it is very much 
used, in the form of rectifiers, for changing alternating to direct electrical 
current. During the past few years there has been an increasing demand 
for lamps which are rich in ultra-violet radiation, which is useful for 
photographic and medical purposes, as, for example, the sterilisation of 
water, milk, etc. This requirement is met by the mercury vapour lamp, 
for the ultra-violet spectrum of mercury is particularly intense ; lamps 
used for this purpose must be made of quartz, since ordinary glass absorbs 
ultra-violet radiation. Then, again, the mercury spectrum is extremely 
useful in spectroscopic work as a reference spectrum. 
In the best types of mercury vapour lamps and rectifiers at present on 
the market, the arc is started by tilting the lamp or rectifier, either by 
hand or automatically. Now, this tilting arrangement is cumbrous, and is 
often very inconvenient. This is found to be especially the case when one 
is dealing with lamps used for scientific purposes. For example, in mak- 
ing measurements on the Zeeman effect, an ordinary mercury high-tension 
vacuum tube in most cases does not form a sufficiently strong source of 
* For history, see von Recklinghausen, “ Ueber die Quecksilberdampflampe von P. C. 
Hewitt,” Elektrot. Zs., p. 492, 1902. 
t Maurice Leblanc, “Experiences de M. Cooper Hewitt sur les tubes a vide,” Journ. de 
Phys. (4), 4, p. 416, 1905. 
I Leo Arons, “ Eine Amalgamlampe mit reichem Linienspektrum,” Ann. d. Phys. (4), 
23, pp. 176-178 ; 0. Bussmann, Elektrot. Zs ., vol. xxxviii., 1907 ; H. E. Ives, “White 
Light from the Mercury Arc and its Complementary,” Bull. Bureau of Standards, vi. p. 265, 
1909. 
