October 22, 1891] 



NATURE 



5^7 



the rule with reference to the wiring of a house, " It 

 should show an insulation resistance of at least "i meg- 

 ohm per lamp," since this wbuld make the insulation of an 

 installation the higher the greater the number of lamp- 

 holders, whereas of course, as a matter of fact, the very 

 reverse is the ciase. 



Chapter iv., on "Arc Light Wiring and Fitting," is 

 full of practical suggestions ; the instructions on the 

 trimming of arc lamps, and the precautions that ought to 

 be adopted in order to keep arc lamps in good working 

 order, will greatly help the young engineer when he is 

 first put in charge of arc lamps. It is a pity, however, 

 that when the author is speaking of supplying constant 

 current to a variable number of arc lamps running in 

 series, he should say, " but the shunt or compound-wound 

 machines are supposed to regulate themselves, which they 

 very often fail to do." For we never heard of a compound- 

 wound machine, still less of a well-made shunt machine, 

 which professed to produce a constant current when the 

 external resistance was varied; And this mistake is em- 

 phasized in the next section, on running arc lamps in 

 parallel, since, although it is quite rightly said of the 

 attendant, that " his chief care is to keep the potential 

 diference between the leads the same,'' Mr. Urquhart 

 states, " This is usually effected in part by the dynamo 

 itself when a shunt-wound machine is used, or by regu- 

 lating the speed " ; and he makes no reference here to the 

 use of a compound-wound machine, as if it were not the 

 special function of this type of machine to keep the 

 potential difference between the mains constant. 



There is a good illustration on p. 107 of the Thomson- 

 Houston lightning arrester, with an explanation of its 

 construction, but no hint is given that the electric arc pro- 

 duced by the lightning flash is magnetically blown out 

 and thus extinguished. And in the large perspective 

 illustration of a Thomson-Houston transfomier, given in 

 this chapter, the thickly-insulated leads are shown with a 

 thick copper conductor inside them, while the lightly- 

 insulated leads have a thin conductor, and since, in the 

 description of a transformer, it is not stated that, besides 

 transforming from a high to a low potential difference, 

 this apparatus also transforms from a small to a large 

 current, it would be quite possible for a beginner to read 

 this book, and wonder why people went out of their way 

 to construct dynamos to produce one or two thousand 

 volts, and then had to employ special apparatus at the 

 consumers' premises to lower this high potential dif- 

 ference. "It is usual to put the secondary circuit to 

 earth," probably expresses the author's view (as it also 

 does the reviewer's) of the proper way to guard against 

 accidents being produced by a contact between the 

 primary and secondary circuits of a transformer, but it 

 certainly does not represent the ordinary practice. 



The name " impedance coils " is suggested for in- 

 ductive coils used to diminish a varying or an alternating 

 current ; but the necessity for this name arises from the 

 expression "choking coils," which is commonly used in 

 this sense, having been wrongly employed by the author 

 for any kind of resistance coils, such as, for example, a 

 non-inductive resistance used with a steady current. 



Chapter v., on " Wiring for Incandescent Lamps," 

 abounds in useful hints, and is illustrated with several 

 NO. 1 147, VOL. 44] 



well-executed woodcuts. Admirable, however, as may 

 be the switches, fuses, &c., constructed by Messrs. Wood- 

 house and Rawson, the succession of illustrations with 

 the names of that firm underneath tends to give the im- 

 pression that there are no other manufacturers of such 

 apparatus. Surely the weighted fuses made by the Acme 

 Works, the switches of Messrs. Siemens — which provide 

 a metallic circuit for the current but expend the flash, pro- 

 duced by opening the circuit, on carbon contacts — and 

 the S switches of Messrs. Crompton, were worthy of a 

 reference. 



If the well thought out precautions detailed in " Methods 

 for Running Wires" had been followed in all the wiring of 

 houses that has been carried out during the past few years, 

 we should not have heard of those very justifiable com- 

 plaints of occupiers who, after taking the lease of a hcruse, 

 temptingly described in the agent's list as fitted through- 

 out with the electric light, find that they have to entirely 

 re-wire the house before the insurance office will allow 

 the current to be turned on. We thoroughly agree with 

 the author that " There is one leading maxim for a con- 

 tractor putting in electric light, and it is to avoid contracts 

 that do not allow of the best class of material and labour 

 being used throughout." We should also like to impress 

 on the general public that the plummer, or the carpen- 

 ter's handy man, is not, as they seem to think he is, any 

 more capable of fitting up an electric installation than he 

 is of setting a broken leg. 



We do not understand why, as a definition of " cleat 

 wiring," Mr. Urquhart says, "This means uncovered 

 wires run &c." : surely cleats are frequently employed to 

 hold down covered as well as uncovered wires. On p. 

 185 the temperature is not stated at which "the ohm is 

 the resistance offered by a column of mercury i square 

 millimetre in cross-section and 106 centimetres long." 

 Power and work are said to be synonymous, and foot- 

 pounds said to be analogous with volt-amperes. The 

 output of 1000 watts "is called under the Board of Trade 

 regulation a kilowatt^'' whereas the late Sir William 

 Siemens, and not the Board of Trade, originated this 

 name. " As lamps are now made, each would probably 

 give a light of 20 candle-power, the watts per candle- 

 power being 25." Would that we could buy glow lamps 

 which had a decent life, while needing only 2"5 watts per 

 candle. . 



Sir William Thomson's rule about the right sectional 

 area to give to a conductor " is only a suggestion made 

 for the protection of buildings from fiie." We thought 

 everyone knew that it was a rule for settling the thickness 

 of the conductor with v/hich maximum economy could be 

 obtained. 



The rules about jointing leads are exact and valuable ; 

 we do not, however, like the general rule of using the 

 body of a chandelier itself to serve as the return, and we 

 think this rule ought to be followed only when the return 

 wire is throughout the installation an uninsulated one. 



Chapter vi. gives a good resume of the pros and cons 

 regarding the use of the body of an iron ship as the 

 return for ship lighting ; while chapter vii. gives the sub 

 stance of the rules issued by the Institution of Electrical 

 Engineers, in connection with fire risks and danger to 

 life. 



