May 6, 1887.] 



SCIENCE. 



431 



cussion of the shots threw the dust into the air, 

 and the flame of the shots ignited it. Gunpowder 

 is in daily use in the collieries, but usually on the 

 working face, where there is insuflScient dust to 

 start an explosion. In every case but one, how- 

 ever, the shots causing the explosions were fired 

 where the miners were enlarging the main road- 

 way, and where the dust had been quietly accu- 

 mulating for years. The fresh air passing these 

 points at the times of the explosions varied from 

 twenty-three thousand to sixty-one thousand cubic 

 feet per minute, so that any accumulation of fire- 

 damp was impossible. Dust in the air may be 

 ignited by an open light, but not by a safety- 

 lamp. One of the curious features of the dust- 

 explosions is, that they exhibit but little force or 

 violence near the point of origin, but seem to re- 

 quire a distance of from fifty to one hundred 

 yards in which to gain headway. Once initiated, 

 the explosion is self-propagating, and rapidly in- 

 creases in violence ; the normal condition, after 

 an explosion is fairly established, being (1) a wave 

 of air preceding the explosion and filling the air 

 in the roads with coal-dust, (2) flame following 

 instantly into compressed air charged with dust. 



Various popular ideas about explosions, such as 

 that they ' face the wind ' or travel against the 

 fresh air, favor the coal-dust theory. 



Under the head of remedial measures, the 

 authors of the report note that wateiing the road- 

 ways, which has been practised for many years 

 as a mere matter of convenience, is of little avail 

 as a means of preventing explosions, since the 

 upper dust in every instance is left undisturbed. 

 Gunpowder should not be used in dusty places 

 without first thoroughly dampening the dust. 

 The accumulation of dust in the roads may be 

 diminished by reducing the velocity of the air, 

 which can be done by enlarging or doubling the 

 roads ; by reducing the speed of the coal-cars ; or 

 by wetting or covering the loaded cars. Exten- 

 sive dust- explosions could be prevented by keeping 

 occasional sections of the roads thoroughly wet. 



Since the dryness of the mines is due mainly to 

 their high temperatures, a large volume of air en- 

 tering at 40°, and raised in its course to 70", ex- 

 ercising an enormous drying power, the following 

 more drastic remedy is also suggested : to raise 

 the air entering the mine to the temperature of 

 the mine, and saturate it with moisture. It could 

 then exercise no drying power, and the natural 

 moisture of the mine would come into play, 

 changing dry mines to damp mines. The princi- 

 pal objections to this plan are the expense, and 

 the greater discomfort to the miners of working 

 in warm, moist air. 



A more recent contribution in the Proceedings 



of the Yorkshire geologic and polytechnic society, 

 for 1886, recognizes the great importance of coal- 

 dust in colliery explosions, and shows, that, con- 

 trary to the generally accepted theory, important 

 explosions are much more likely to occur when 

 the barometer is high than when it is low. The 

 explanation is, that, while a high or rising barom- 

 eter tends to prevent the escape of gas from the 

 coal, it is also usually accompanied by a dry at- 

 mosphere, which renders the coal-dust lighter and 

 more inflammable. 



ELECTRIC RAILROADS IN THIS COUNTRY. 



An interesting article on electric railroads in 

 the United States, by T. C. Martin, appeared in a 

 recent issue of the Railroad gazette. The progress 

 already made in the application of electric energy 

 as a motive power for street-railroads, as reviewed 

 in Mr. Martin's article, cannot fail to be encourag- 

 ing to all engaged in the development and exploi- 

 tation of inventions in that particular field of in- 

 dustry. Nor is it without interest to scientific 

 men and the public generally. One electric road 

 in Baltimore, equipped by the Daft company, has 

 been in siiccessful and profitable operation about 

 two years. A road in Los Angeles, Cal. , built by 

 the same company, has been running several 

 months, and is soon to be extended to nearly 

 double its present length. This company is also 

 constructing and equipping electric railroads in 

 Pittsburgh, Penn., and Orange, N.J., and will 

 construct others at Mansfield, O., and Ithaca, 

 N.Y. 



The Van Depoele company of Chicago is able 

 to show a good record in the matter of electric- 

 railroad construction. Roads using its system of 

 electric propulsion are running at Port Huron and 

 Detroit, Mich.; Appleton, Wis.; Windsor, Ont. ; 

 Scranton, Penn.; and Montgomery, Ala.; which 

 last-named city has eleven miles of road in 

 operation. This company is now constructing 

 roads at Lima, O., and Binghamton, N.Y. 



In Denver, Col., there is an electric road, con- 

 structed on what is known as the Short-Nesmith 

 system, in which the current conductor runs in an 

 underground tube, contact being effected through 

 a five-eighths inch slot between the rails. This 

 road crosses eight horse-car tracks, five steam-car 

 tracks, and a two-hundred-foot bridge. 



A three-mile road in Detroit uses the Fisher 

 system of equipment, and a short line in Pitts- 

 burgh is being equipped on the same system. A 

 nine-mile section of road in San Diego, Cal., in- 

 tended for high speed, will be constructed by a 

 company which has just completed a double-track 

 road in Kansas City. These two are overhead 

 conductor roads. A Philadelphia company, which 



