[June> 
358 Analyses of Books. 
Bunsen photometer is of course recommended as preferable to 
that of Rumford, but no standard unit is suggested as more 
constant than the English candle and the French carcel. 
Among sources of power wind is omitted, doubtless from its 
inconstancy. In the fifth chapter, which treats of Dynamo-elec- 
tric Generators, the most efficient machines of the day are 
described and figured. It is prophesied that the dynamos of the 
future, “ though they may not be very much more efficient than 
those of the present day, will probably be of much larger size 
and of simpler construction ” — a very safe forecast. 
The two next chapters treat of Arc-lamps and of Semi-Incan- 
descent and Incandescent Lamps, the advantages of the latter 
as best suited for use in houses and other confined areas. Their 
freedom from flickering is the most important point. According 
to Sir W. Thompson, for one and the same expenditure of power 
an arc-light gives ten times the quantity of light which can be 
obtained from a glow-lamp. In the latter the consumer has to 
steer his way between two evils. If the current is too powerful 
the filament is rendered intensely brilliant, and the economy of 
the light is increased. But the filament is soon worn out, and 
the lamp quickly becomes useless. If the current is too feeble 
the lamp will last for a very long time, but the light is feeble and 
yellow. 
“ Accumulators,” as at present constructed, labour under so 
many defeCts that they are employed only where unavoidable. 
Probably they may be found capable of improvement. In the 
meantime they serve mainly as a type of the modern English 
youth whose education consists in preparing for examinations. 
The secondary battery, like the student, takes up a certain quan- 
tity of power, and gives it out again minus a heavy amount of 
leakage. 
The last chapter is one of great practical importance, as it 
discusses the advantages and the cost of eleCtric lighting. It is 
interesting to find that in several cases, the particulars of which 
are fully known, electricity has proved itself a cheaper source of 
light than coal-gas. The installation which Mr. W. Crookes, 
F.R.S., has adopted in his house, for the efficiency of which we 
can bear witness, effeCts a saving of £4 17 s. 6 d. yearly, although 
the dynamo and the gas engine, from the nature of the case, 
work under serious disadvantages. An important consideration 
is that incandescent lamps do not vitiate the air in the slightest. 
Ceilings are not blackened ; books, pictures, upholstery are not 
injured, and the risk of fire is decreased. 
We think that this little book will encourage many persons to 
try the experiment of introducing the eleCtric light into their 
houses, and will thus do a good work. 
