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XIII.—ON A NEW FORM OF ELECTRICAL CONTACT- 
MAKER, FOR ASTRONOMICAL AND OTHER CLOCKS, 
BY HOWARD GRUBB, w.r., F.z.a8., WC. 
[Read February 18th, 1878.] 
THE object of a series of experiments was to obtain a system of 
electrical contacts (suitable for attachment to a delicate clock), 
free from the well-known existing defects. 
The conditions desirable to be obtained, are :— 
1st.—Certainty of contact. 
2nd.—Precision of contact, as regards duration. 
3rd.—F reedom from possibility of causing any irregularity 
in rate of clock to which it is attached. 
4th.—Permanence in—i.e., freedom from possibility of 
requiring any repairs or adjustments for a considerable 
period of years. 
The author submits that, with exceptionof the system now about 
to be described, he has met none thoroughly satisfactory. He 
has found that any mechanical contact possessing the first quali- 
fication must have some slight “ rubbing,” as well as “ touching ” 
or “contact action,” to keep off the slight film of oxide which 
inevitably forms on the surface of the platinum or gold; and this, 
no matter how slight, at once introduces a variable friction into 
the clock, and destroys qualification No. 3. 
On the other hand, mercurial contacts, though very precise and 
satisfactory on the first start, soon deteriorate, from the oxidation 
which takes place so rapidly on the surface. 
This being the case, it occurred to the author that clearly the 
proper course to take would be to use a mercurial contact, an 
vacuo, or at least with absence of all oxygen, and this has been 
for so far attended with complete success. The author has tried 
many forms of such contacts, with the kind assistance of Mr. C. 
H. Gimmingham, to whom he is indebted for many useful sugges- 
tions and modifications. 
Fig. 1 represents a section of one of the contact-makers, blown 
in glass by Mr. Gimmingham. A, B, C, are the three platinum 
terminals, A is always in contact with the mercury ; and if this 
