432 



SCIENCE. 



[Vol. XIII. No. 331 



lines of force, the resistance of a wire to an electric current. The 

 shortest possible length for the magnetic circuit is obtained by giv- 

 ing a circular form to the machine. The result shows that the 

 machines have come out very close to their estimated power, the 



claimed to have considerable advantage over most slow-running 

 fans. Two of these fans have been successfully employed to ven- 

 tilate a hall 100 feet square, being placed opposite each other, and 

 both used as exhausts. Another method employed is to place one 



-THREE-HORSE-POWER C. 



actual number of volts developed being 109 against 1 10 in a 3-horse 

 power motor. It has been aimed at to eliminate Foucault's cur- 

 rents and undue heating. 



of these fans at either end of a hall, one running as an exhaust, and 

 the other forcing air in. 



WATER-FILTRATION. 



FIG. 3.— THE C. & C. COMPANY'S MOTOR AND EXHAUST FAN. 



Another application of this motor is to the driving of ventilating- 

 fans. Fig. 3 shows a J-horse-power incandescent motor fan outfit. 

 This apparatus at a speed of one thousand revolutions a minute is 



Probably at no time has the condition of the water-supply of 

 our cities and towns received more attention than at present, and 

 perhaps no one thing has conduced to this state of affairs more 

 than the discovery that certain salts contained in the earth act as 

 renovaters of all so-called " spring " waters, purging them, so to 

 speak, of the foul matters held both in solution and in suspension. 



Up to the time of this discovery, it was thought that the earth 

 acted merely as a filter or strainer on a large scale, and that each 

 grain or atom of earth acted Us part toward opposing or arresting 

 mpurities in the passing water ; in other words, that only mechani- 

 cal straining or filtering took place, and nothing more. 



Multitudes of filters have been made and put in operation in all 

 ages and countries with the expectation of seeing the water emerge 

 from them as pure and sparkling as from a good " spring," and 

 the greatest surprise has been manifested at the failure to secure 

 the same results when apparently every condition was supplied. 

 The question remains, " Was every condition supplied.'"' Modern 

 science answers, " No." 



The peculiar action of the above salts upon the portion of im- 

 purities said to be held in solution is well illustrated by the effects 

 produced by dissolving soap in a water of great (so called) hard- 

 ness. The white flakes that almost instantly appear are composed 

 not alone of dissolved soap (for soft water would not show such 

 individualized flakes), but a mixture of soap and some substance 

 hitherto held in undisturbed solution in the water, but now with- 

 drawn from that condition and floating about in mechanical sus- 

 pension. 



It will be plain that if this soap-treated water was now poured 

 into the earth at one point, and made to emerge at another some 

 distance off, it would be found purged of not alone the soap it con- 

 tained, but also of the modicum of foreign matter held in its 

 embrace, and which went to make up the quality of hardness 

 spoken of. 



