654 REPorT—1883. = £. 
Swen 
/ : Resistance -Resistance | Difference 
Matexal before Heating ' of Leads after 24 hours ~ 
ohms ohms > 
No. 1. Commercial Tin wire . i 815 8 —003 
3 2) Lead, soft . ; 4 4 “835 8 -~*005 
5» 8. Copper, soft ; : 5 “81 8 No change 
» 4. Pure Tinfoil 3 c 4 86 8 No change 
» 5. Tin and Lead alloy . . ‘8ST 8 » —'160 
,, 6: Albo alloy, in foil - *835 8 No change 
, 7, Aluminium and Tin alloy . "82 8 +0008 
The resistances were in all cases taken at the temperature of the air, which 
averaged 69°, 
The sign — shows that the metal decreased in resistance, and + that it 
increased after continued heating. Nos. 1 and 3, tin and copper, were found to 
‘scale when heated. 
A change has been noticed where high tension currents have been sent through 
a pure copper wire for some time—the wire in the armature of a Siemens’ machine, 
which came under the notice of the author, appeared to be brittle, and gave a fracture 
unlike pure copper. 
The necessity of good electrical connections is very great, also special arrange- 
ments of switches and contact-breakers which, when left in unskilled hands, are 
liable to cause dangerous heating or an are. 
Short circuit is the danger which may be caused by badly arranged wires ; most 
likely a conflagration will ensue unless the remedy suggested by the Fire Risk 
Committee and the Board of Trade is adopted—of having a cut-out or fusible 
plug in the circuit which gives way when the current is in excess. These should 
be arranged to melt if the current is more than ten or fifteen per cent. of the 
working strength, otherwise absolute safety is not arrived at. Ordinary lead or tin 
wire cannot-be used except for very small currents, as on fusing the metal is 
scattered in a globular form, when it is liable to cause fire, The plan adopted by 
the author is to take pieces of foil arranged like the leaves of a book; the thinness 
of the foil causes it to-be almost volatilised when melted. The material found to 
be the most reliable is a special alloy of aluminium, termed Albo metal, which is 
onieenely tough, and can be worked much nearer to its fusing point than tin or 
lead. 
The safety of an electric light installation is only insured by testing, which 
should be done by a current of higher electro-motive force than it is intended 
to use. 
When the work has been properly supervised no trouble should be experienced, 
and the electric light may be said to be much safer than gas, as it is free from those 
accidents which are due to a servant's carelessness, or by leakage of the pipes. 
Whatever danger there is with electric lighting is entirely localised to the generating 
station where the dynamos and engines would be under constant, supervision. 
TUESDAY, SEPTEMBER 25. 
The following Papers were read :-— 
1, Improved Current Meters and Mode of taking Sub-surface Observations.! 
By Professor H. S. Here Suaw. ee ie 
The difficulties in the way of taking current-meter observations on sub-surface 
velocities in a river channel or tidal estuary are well known, and Have led to the 
} Published in extenso in the Hngincer, October 26, 1883. 
