TRANSACTIONS OF SECTION G. 757 



generators from the switch station ; and the number connected on to the network 

 being varied to suit the load, it is possible to always work the transformers at a high 

 efficiency. A small battery situated at the switch station is used to supply the 

 small day and night loads, thus enabling the Central Station to bo entirely shut 

 down for a great portion of the twenty-four hours. 



The figures for 1893 show that the total efficiency of the system was GI-62 per 

 cent., and the efficiency of the motor generators was 74-44 per cent., including 

 losses in mains and resistances. This is not so high as it will be in the future, 

 when the lamps are more evenly distributed over the area. The battery efficiency 

 was 5064 per cent. The actual coal used throughout the year works out to 

 6-83 lb., or -718 penny per unit sold, which is a very good result, as only slightly 

 over 100,000 Board of Trade units were metered. The oil, waste, water, anil 

 general engine-room stores tvork out to -0657 penny per unit metered. The total 

 number of lamps installed at the beginning of the year was 4,041, which increased 

 to 7,01 2 by the end of the year. As the great proportion of supply is taken up by 

 colleges, the term-time is the only part of the year when anything like a load can 

 be obtained, and the load factor is only 631 per cent. 



The revenue during the year under notice was 10s. lid. per 35-watt lamp 

 installed. 



4. On a Sjxcial Chr'onoc/raph. 

 By Henry Lea, M.Inst.C.E., and Robert Bragge. 



In his capacity as electric inspector for the city of Birmingham the duly ot 

 one of the writers is to test the accuracy of the electric meters used in that city. 

 The test involves an accurate measurement on the one hand of the current of 

 electricity passing through the meter, and on the other band of the period of time 

 during which the current of electricity efl'ects a certain number of revolutions of 

 the meter armature. 



For the electrical measurements he selected a Crompton potentiometer, but 

 as his chronograph was not accurate enough he drew up a specification upon 

 which the English Watch Company built the chronograph exhibited to the meeting. 

 The ideal chronograph is one with a perfectly divided dial, an absolute prompt 

 start, a definite stop at zero, and a continuous or running motion of the hand. 



The test-room chronograph under notice is not intended for use as a watch ; it 

 is purely and simply a micrometer applied to time, and therefore it has only two 

 3)ointers — one from the centre, giving seconds and their fractions, the other placed 

 halfway between the centre and circumference, showing minutes up to sixty. The 

 dial of aluminium, being engine divided, is mechanically perfect; and being of 

 large size, 2j inches of sight, the divisions of ten to the second are clearly 

 defined. 



The prompt, absolute start is obtained by dispensing with all intermediate gear- 

 ing and relying on the main train of wheels impelled by the ordinary mainspring. 

 The starting lever not only releases the balance-wheel, but at the same time by 

 the momentary contact of a light spring blade impels the wheel in the required 

 direction. 



The absolute stop at the end of an observation is obtained by the frictional 

 •contact of the aforesaid spring blade with the edge of the balance-wheel. 



The absolute stop at zero is obtained by fixing upon the axis of the seconds 

 "wheel a collet carrying a blade. Upon the top of the movement there is a lever, 

 •which, during the period of an observation, is held back ; but when the observa- 

 tion is concluded it is set free by a push of the button, and falls to a point where 

 it crosses the path of the blade already referred to, and stopping the wheels brings 

 about the absolute stop we require. 



The last thing requisite is for the seconds hand to have a continuous run. 

 Everything tried up to the present has had a tendency to accelerate its rate, and 

 is therefore inadmissible. The lever escapement has been adhered to, and by 

 using hard stone jewellings, and by observing great accuracy in the angles of the 

 pallets, the makers are enabled to double the ordinary number of beats — 36,000 



