734 REPORT — 1902. 



The staff may be any number of feet in length, and may be graduated according 

 to any pattern which the user finds convenient. It differs essentially from the 

 ordinary levelling staff in having a shoe which slides on the staff at the end with 

 the maximum graduatioas, and which can be extended and fixed at any particular 

 hundredth of a foot so as to lengthen the staff by the amount of that extension. 



The method of employing it is as follows : — 



Having set up the level, the height of the instrument or ' collimation level ' is 

 obtained, as usual, by adding to the value of the ' bench marli ' on which the staff 

 is held the reading seen on the staff. The shoe is now extended to the amount of 

 the decimals in the collimation level, and in the field-book, beneath the collimation 

 level, is written the ' datum level,' which is the total length of the extended staff 

 less than the collimation level. The 'datum level' consequently is a whole 

 number without decimals. All other observations from this position of the level 

 are now taken with the staff inverted, i.e., the shoe on the ground, and the reduced 

 level is obtained by adding the reading to the datum level. 



The amount to which the shoe is extended only has to be altered when the 

 collimation level is altered, i.e., when the instrument's position has been altered. 

 The booking as reduced levels of a large number of observations from one position 

 of the level is extremely simple and rapid. 



8ATURBAY, SEPTEMBER 13. 

 The Section did not meet. 



MONDAY, SEPTEMBER I.'). 



The following Papers were read : — 



1 . The FuUire of the Telephone in the United Kingdom. 

 By J. E. Kingsbury. 



2. A New Magnetic Testing Instrument. By F. Holden. 



3. The Electrical Conductivity of certain Aluminium Alloys as affected by 

 Exposure to Loridon Atmosphere.'^ By Professor Ernest Wilson. 



This paper deals with the effect upon electrical conductivity of exposing light 

 aluminium alloys to London atmosphere. The author pointed out that if commer- 

 cially pure aluminium be alloyed with a small percentage of copper for the purpose 

 of increasing its tensile strength exposure diminishes electric conductivity, possibly 

 by electrolytic action pitting the surface. If, in addition to the copper, a small 

 percentage of nickel be added, no such effect occurs, and the tensile strength is 

 increased. The discovery that metals which alloyed alone with aluminium may 

 produce unfavourable effects, but in combination prove beneficial, may have 

 practical importance in other than electrical branches of engineering. The 

 physical properties of aluminium alloys are still little understood, and the 

 subject is of great interest to engineers in general. 



4. Some Electrical Instruments, By M. B. Field. 



Four instruments were exhibited and briefly described. The first was a volt- 

 meter for a three-wire circuit which was compensated for the voltage drop in a 



' See the Electrician, September 19, 1902. 



