686 REPORT—1904. 
half of the percentage of manganese, or, in other words, when the alloy contains 
one atom of aluminium to one atom of manganese. 
It may be added that the alloy exhibited is, unfortunately, very brittle, and all 
attempts to forge it, cold or hot at various temperatures, even only at dull red, 
have been unsuccessful. 
6. Indicator Tests on a small Petrol Engine. 
Sy Professor H. L. Cauuenpar, 7.2.8. 
WEDNESDAY, AUGUST 24. 
The following Papers were read :— 
1. Side Slip in Motor Cars.' 
By Horace Darwin, £.2.8., and C. V. Burton. 
2. An Electric Temperature Alarm.2 By Horace Darwin, F.R.S. 
Os 
The Electrical Conductivity of certain Aluminium Alloys as affected by 
Exposure to Londow Atmosphere, and a Note on their Micro-structure. 
By Professor Ernest WILson. 
This paper dealt with the effect upon electrical conductivity of exposing light 
aluminium alloys to London atmosphere. During three years’ exposure the 
copper-aluminium alloys have gradually diminished total conductivity to a greater 
extent the greater the percentage of copper. Of the nickel-copper-iron aluminium 
alloys, which show such remarkably increased tensile strength as compared with 
good commercial aluminium, those which are richer in nickel have diminished total 
conductivity least. ‘The manganese-copper aluminium alloys have suffered com- 
paratively little diminution in total conductivity, and one of them has compara- 
tively high tensile strength. A 1:2 per cent. iron aluminium alloy has shown very 
little diminution in electrical conductivity. It was thought that an examination of 
the structure of these alloys by aid of micro-photography might throw some light 
on the great difference which exists between some of their physical properties. For 
instance, a nickel-copper aluminium alloy has 1°6 time the tensile strength of 
ordinary commercial aluminium. Under a magnification of 800 diameters practi- 
cally no structure could be discovered. Considering the remarkable crystalline 
structure exhibited by ordinary commercial aluminium near the surface of an ingot, 
when allowed to solidify at an ordinary rate, the want of structure in these alloys 
must be attributed to the process of drawing down. The inference is that the 
great difference which exists between their tensile strengths and other qualities is 
not due to variation in structure. The experiments in micro-photography have 
been carried out by aid of a portion of the Government grant voted to the author 
by the Council of the Royal Society. 
4, The proposed Barrage of the River Thames. 
By James Casey. 
Any engineering scheme that offers a solution to the many problems involved 
in attempts to remove the inconveniences and difficulties attending the navigation 
of the river Thames, with a view to the proper control of the enormous volume 
1 Published in Engineering, September 9, 1904. 
2 Published in Lngineering, March 10, 1905. 
