January 20, 19 16] 



NATURE 



577 



The meeting of the Science Teachers' Association 

 was largel}' attended by science mistresses, the propor- 

 tion of men present being small. Miss Durham gave 

 a lucid account of Mendelian laws, and described suc- 

 cessful researches on the heredity of mice, canaries, 

 and primroses. The association has recently formed 

 small committees with the object of making it easier 

 for teachers in schools to follow the growth of various 

 branches of investigation. During the past year some 

 papers have been read and circulated among members, 

 of which we may instance "Development in Chemistry 

 during the War," by Miss S. T. Widdows. Member- 

 ship of the association is open to science masters, and 

 it is hoped that those who realise the value to the 

 nation of science in the schools and desire to promote 

 efficienc}'^ by combined effort will communicate with 

 the honorary secretary, North London Collegiate 

 School, Sandall Road, N.VV., with a view to member- 

 ship. 



These notes may finish with a quotation from the 

 address on "The Teaching of Imperial History," by 

 Sir Charles Lucas, to the Historical Society: — "What 

 differentiated modern from ancient and medieval 

 history was science and scientific invention. Scien- 

 tific teaching has never been treated as the central and 

 omnipotent force in the life of the nation, but demo- 

 cracy is the direct result of scientific invention and not 

 of Acts of Parliament. The history of the past fifty 

 years has been a record of the manner in which scien- 

 tific invention has helped us by federating the different 

 groups of Dominions." G. F. Daniell. 



MODERN SYSTEMS OF INDEPENDENT 

 LIGHTING AND HEATING A 

 III. Lighti)ig by Electricity. 

 T^HE problems of lighting country houses by elec- 

 -'■ tricity vary greatly according to the size of the 

 installation. The owner of a large country house has 

 the advantage of being able to afford a competent 

 engineer, and, since he generates on a large scale, he 

 may obtain electricity at a relatively cheap rate, 

 in some cases even at a lower rate than that ordinarily 

 allowed by the local supply company. On the other 

 hand, many country mansions are but little used by 

 their owners during a great part of the year. This 

 intermittent demand for electricity is a drawback, as 

 it does not conduce to economy, and makes it difficult 

 to maintain the plant in a state of continued efficiency. 

 It is naturally inefficient to have a large engine and 

 dynamo running to supply only a few lamps. 



In small houses, on the other hand, the demand, 

 though comparatively small, is more constant. It is 

 probable that in such cases, taking due account of the 

 running cost of generation, the interest of the original 

 cost of the plant, and the repairs to the plant and 

 batteries, the cost of generation will probably not be 

 less, and may be more, than ^d.-6d. a unit ; however, 

 with some of the most recent automatic types of plant, 

 generation at a rate of 2d. per unit is said to be prac- 

 ticable. 



In a large country house the source of power may 

 be a steam engine or an engine run by suction gas or 

 oil gas. When water-power is available a water- 

 turbine would probably prove the most economical 

 and convenient source of energy. It is also necessary 

 to instal a battery of accumulators in order to provide 

 a steady voltage, and the usual arrangements for the 

 control of the supply, including the switchboard, 

 measuring instruments, resistances, etc., must be pro- 

 vided. It is generally agreed that the current of 

 accumulators alone gives the most steady source of 



1 Continued from p. 553, 



NO. 2412, VOL. 96] 



supply, and accordingly the battery may be used for 

 the lighting during the evening and charged during 

 the day. Special arrangements may also be made to 

 run the lights from the battery and dynamo in parallel. 

 One advantage of a large battery, as well as a dynamo 

 capable of supplying the entire load, is that one has 

 an emergency supply in case of the engine breaking- 

 down. The maintenance of the battery in good order 

 is one of the chief difficulties in those installations 

 where Httle current is used during the summer. 

 Accumulators ought to be charged and discharged at 

 regular intervals. There are even cases in which it 

 is necessary occasionally to discharge the battery 

 through a resistance as an " artificial load " during 

 the summer, thus wasting current in order to keep the 

 cells in good order. 



It is very difficult to quote definite figures of the 

 cost of country lighting installations ; generally speak- 

 ing, the cost for a fairly large installation, including 

 the plant, battery, and switchboard of mains to the 

 house, might work out as follows : — 



Initial cost of 

 plant, etc. 



100 



130-150 



No. of lights 

 (.6c.p.) 



25-30 

 40-50 

 80-100 

 200 



150-170 

 200-220 



To this must be added the expenditure on fittings 

 and the cost of internal wiring. The cost of wiring 

 in country districts may be as high as 255. to 35s. a 

 point. It is remarkable how the expenditure under 

 this heading varies, especially in converting old 

 mansions, where unexpected obstacles in wiring, due 

 to the structure of the building, are often met. In 

 many cases it is also desirable*to allow a fair margin 

 in estimating as to the size of the plant, as it is often 

 useful to have electricity available for other purposes, 

 such as heating radiators and driving pumps and 

 agricultural machinery, etc. In large country houses 

 with a big plant, electric radiators are frequently used 

 for heating rooms. The small consumer, however, 

 will scarcely go to this length, but may make good 

 use of small heating accessories, such as electric 

 kettles, irons, etc. 



The possibilities of electricity for lighting a country 

 house have been much simplified by the introduction 

 of the metal filament lamp, the improved efficiency of 

 which as compared with carbon filaments makes it 

 possible to light a house of a certain size with a much 

 smaller plant. It is usual to work at a pressure of 

 50 volts for lighting, as this enables metal filament 

 lamps to be used under the most efficient and 

 economical conditions. Small candle-power lamps 

 having stout filaments and exceptional durability are 

 available for 50 volts. On the other hand, if power 

 is to be transmitted a considerable distance the cost 

 of mains becomes an important item, and it may be 

 desirable to raise the pressure to no volts in such 

 cases, so that the current to be carried by the cables 

 may be diminished. 



To the small householder, the care of the plant is 

 naturally an important item, and he may have to 

 rely to a great extent on his personal efforts in this 

 direction. It is therefore essential that a plant for 

 small users should be as simple and easy to operate 

 as possible. For small installations, the usual prac- 

 tice is to employ a dynamo driven by a small petrol 

 engine. During the last few years there have been 

 great improvements in the simplification of such 

 plants, which have reduced the attention necessary to 

 a minimum. In particular, devices have been adopted 

 to enable the plant to run automatically, ceasing to 

 generate when all the lamps are turned off, in the 

 same way as a petrol-air gas plant. 



