TRANSACTIONS OF SECTION G. 625 
arrangements devised by the writer. A short account of previous tests on resist- 
ance alloys was followed by a description of some recent tests on modern 
resistance materials obtained by Mr. J. H. Baugh and tested by Mr. A. C. Jolley 
in the laboratories of the Northampton Institute. The alloys best suited for 
standards, owing to their low temperature coefficient, are those of copper and 
manganese, or of copper and nickel. The former has the advantage of low thermo- 
electric force against copper, but a very curved temperature variation. The copper 
nickel alloys, on the other hand, have a nearly regular temperature coefticient 
which may be either positive or negative, but their thermo force is very high. 
The desirable features of standard coils were mentioned, emphasising the 
matter of low and uniform temperature variation and good heat radiation, and 
it was pointed out that most existing standards are deficient in these respects 
and in the design of their terminals. 
The author proposed an open wound coil with special form of terminals, and 
wound with a wire of copper nickel or similar alloy, in which the temperature 
variation is compensated, either by joining two such wires of positive and negative 
coefficient in series or in shunt with each other, or by coating a wire of nega- 
tive coefficient with a suitable proportion of a metal or alloy having a positive 
coefficient. By suitable selection it may be possible to compensate both the first 
and second terms in the temperature variation. It has been found possible in this 
way to obtain a coil having a temperature variation probably less than one part in 
a million for 1° Centigrade over the ordinary working range of temperature. 
The bridge method either in the single or double form was considered best for 
standardising purposes, and a comparison made of the slide wire bridge in its 
various forms with that of the Reichsanstalt. A description was given of a new 
bridge in which the advantages of both forms have been combined, this bridge 
being capable of being used either as a single or double bridge for resistances of 
any value, with or without potential contacts, and of any gauge. The readings 
can be taken either by shunting or on a double slide wire, and in the latter case 
the difference between the coils is read directly over a range from 1 to 5,000 
millionths. A special form of ratio coil, enabling step-up or step-down measure- 
ments to be made, was also described. 
WEDNESDAY, AUGUST 7. 
The following Papers were read :— 
1. A Machine for Weighing the Forces on a Cutting Tool.' 
By Joun F. Brooks. 
The object of the machine is to measure the three co-ordinate components of 
the force on a cutting tool while in the act of cutting metals. 
The tool, fixed in a holder, forms part of a simple lever carried by a thin 
diaphragm of steel, 
This device gives a universal frictionless pivot when used for very small dis- 
placements, 
The location of the lever is effected by means of electrical contacts in circuit 
with telephone receivers, 
Weights are used to balance the forces, 
gate apparatus is capable of measuring maximum, minimum, as well as mean, 
values, 
The position of the centre of pressure may be found by two or more experi- 
ments, 
The paper was illustrated by diagrams, showing the values of the forces on 
tools with cutting angles of 65° and 70° when cutting cast iron and mild steel, 
with small cuts at moderate speeds. 
" Published in ewtenso in Engineering, August 23. 
1907, 88 
