August 29, 1902.] 



SCIENCE. 



341 



lights knows that the familiar incandescent 

 lamp is made in several sizes of different 

 brightness or candle-power. The common 

 size yields nominally a light in the direc- 

 tion chosen for rating equal to that emitted 

 by sixteen standard British candles. The 

 light emitted in other directions depends on 

 the form in which the filament is coiled. 

 Now, it is possible for each of two lamps to 

 yield light in the measured direction of 16 

 c. p. intensity, and yet to produce quite dif- 

 ferent total amounts of light. This means 

 that the lamps, although nominally of the 

 same candle-power, are actually of quite 

 different power as producers of general 

 illumination. 



Clearly the only true criterion of the 

 worth of lamps as producers of light is the 

 average light produced in all directions. 

 This value is called the mean spherical 

 candle-power. 



A new form of photometer has been de- 

 vised by Professor C. P. Matthews, of Pur- 

 due University, that gives this value with 

 the ease and simplicity of the ordinary 

 photometric measurement. A double ring 

 of mirrors produces on one side of the pho- 

 tometer screen an illumination proportional 

 to the mean spherical candle-power of the 

 lamp to be tested. This illumination is 

 balanced or equalized against that due to a 

 light of known candle-power at a distance 

 that can be read from a convenient scale. 

 The instrument is adapted to all forms of 

 photometric measurements or incandescent 

 lamps, gas flames and sources of like inten- 

 sity. 



The Proposed Air-ship Contests at the St. 

 Louis Fair: Calvin Woodv^ard, Wash- 

 ington University. 



It is the expressed opinion of many, per- 

 haps the conviction of most people, that 

 nothing ever will be accomplished in the 

 way of aerial navigation that is of perma- 

 nent commercial or social value. It is 



admitted that balloons may furnish valu- 

 able positions for observations in war, but 

 no aii'-ship will ever be able to make trips 

 to and fro, carrying either freight or pas- 

 sengers. With all due respect to such peo- 

 ple, the author is bound to dift'er. They beg 

 the question. He freely admits that the 

 problem has not been solved; that our 

 appliances for the transformation and 

 utilization of energy are at present inade- 

 quate ; even the line along which progress is 

 to be made has not been fully determined; 

 but he has no doubt of the result. It may, 

 and probably will, take many years, but 

 there is plenty of time, and even the wisest 

 of us 'do not know it all.' 



History ought to teach us something of 

 the proper attitude toward unsolved prob- 

 lems. It will be reniembered that a com- 

 mission consisting of the most eminent of 

 the engineers of England headed by Rennie 

 opposed the use of the locomotive on the 

 first complete railroad, but Stephenson per- 

 suaded the owners of the Liverpool and 

 Manchester road, who had expected to pull 

 their trains by cables moved by stationary 

 engines, to offer a prize of .$2,500 for the 

 best locomotive and to open the competition 

 to the world. The result was the entry of 

 five engines, among which was the victorous 

 ' Rocket ' which demonstrated the possibility 

 of a successful railroad locomotive. The 

 result proved the great value of an open 

 competition. 



Scientific men sometimes nod. Professor 

 Lovering, afterwards President of the 

 American Association for the Advancement 

 of Science, when Cyrus W. Field was pre- 

 paring to lay the first Atlantic cable, in a 

 lecture to the author's class at Harvard, 

 proved the utter impossibility of tele- 

 graphic communication under an ocean 

 3,000 miles wide. 



The Executive Committee of the Louisi- 

 ana Purchase Fair believe that progress in 

 aerial navigation is possible and they have 



