456 



SCIENCE. 



At length the Foord Pit was won out, and, with its 

 great pumps and engine?, formed one of the finest coal- 

 mining establishments in America. The ventilation was 

 effected by a large Guibal fan, similar to those used in 

 the Pennsylvania Mines, and capable of circulating 

 120,000 cubic feet of air per minute through the ramifi- 

 cations of the mine. The workings of the Foord Pit, 

 which is nearly i.coo feet deep, extend about 1,800 yards 

 to the north, and 1,700 yards to the south, having an 

 average breadth of -550 yards. The galleries varied in 

 height from 9 to 15 feet, being driven in the upper part 

 of the seam, the lower part being left for later operations. 

 The ventilation through the south side was maintained 

 at the average rate of 25,000 cubic feet per minute. 

 Shortly before the accident referred to, I went entirely 

 through the colliery, in company with Mr. Gilpin and the 

 overman, and we remarked the perfection of the ventila- 

 tion, and the consequent absence of deleterious gases, 

 even in the remotest bords. 



On the morning of the disaster the night watchmen 

 reported the mine to be free from gas, except in small 

 and harmless quantities. From what source, then, 

 originated the series of explosions that began within an 

 hour from the time this report of entire safety was made, 

 and continued at intervals until the mine became a furn- 

 ace, whose flames could be subdued only by emptying 

 into its burning chambers the waters of the adjacent 

 river? Was there some sudden exudation of gas from the 

 solid coal, or was this explosion due to the firing of coal 

 dust from a safety-lamp or the flame of a blast ? 



None of the forty-four men who witnessed the begin- 

 ning of the catastrophe escaped to tell the story or ex- 

 plain the mystery, and those rescued irom more distant 

 galleries had but conjectures to offer. The workmen on 

 receiving the assurance that the mine was free from gas, 

 received their orders, descended the drawing shatt, re- 

 ceived their safety-lamps at the lamp cabin and a part of 

 them went into the north side workings and the rest went 

 into the south side dips and waited for their tools to be 

 sent in for distribution. At this moment the explosion 

 took place that was first noticed at the fan-shaft, where 

 it blew the cover of the fan-drift off, and about one min- 

 ute later it was apparent at the drawing shaft, having 

 traveled in the one case with and in the other against 

 the ventilating current. 



The only additional facts definitely ascertained were 

 gathered by an exploring part led by Mr. Gilpin, who, 

 shortly after the original explosion and at the risk of life, 

 descended into the pit and penetrated as far as the after- 

 damp would allow them to go. The locality where the 

 unfortunata workmen whom they tried to save were 

 known to be was 1,200 yards south of the shaft ; and the 

 point reached by the party was only about 600 yards in 

 that direction. 



It was evident that the flame of the explosion had not 

 reached as far as this, for there were no marks of fire on 

 the dead bodies of men and horses found, nor was the 

 splintered wocd-work charred. They carried two corpses 

 to the surface for examination, and it was found that one 

 of these died of the after-damp, and the other from being 

 dashed against some timber. 



The walls of the galleries had been swept clear of 

 timber, and presented the appearance of having been 

 brushed with a broom. This was due to the passage of 

 great volumes of dust which lay on the floor of the 

 level in waves and drifts, into which the party often sank 

 up to their knees. A similar effect was visible in the 

 mine level, but not to so great a degree ; as it was damper 

 about the floor, and from the effects observed it would 

 appear that, while the explosion passed along each level 

 simultaneously, it had greater power in the lower one. as 

 the doors were blown toward the upper, or main level. 

 Clouds of the finer particles were carried up the shaft, 

 and were swept on into the North-side levels. 



At the lamp-cabin, where the safety lamps were 



cleaned and given to the men after being examined by 

 the shot-firers, an open light had been kept burning for 

 years, as it was considered a safe place, being 

 within a few feet of the bottom of the shaft. But 

 here a secondary explosion took place, demolishing the 

 cabin, burning the horses between the shaft and the 

 cabin, and fatally injuring the lamp-man by igniting his 

 oil-soaked clothing, so that he died in a few days. The 

 effect of the explosion did not extend far into the north 

 side, and some of the men there were ignorant of the 

 disaster until warned by the over-man to leave the pit. 



Secondary explosions caused by extracted, or generated 

 gas, are nearly always in the vicinity of the primary one ; 

 but here is a case where the second was half a mile from 

 the first, with an intervening space of at least a quarter of 

 a mile known to be free from gas, because men were in it 

 with lamps which showed no indications of its presence. 



The ignition of these volumes of dust would, no doubt, 

 have done serious injury to the shafting, had not the 

 latter been wet and indeed saturated with water oozing 

 under pressure through the upper strata into the shaft, 

 and then falling to the bottom ; so that, although else- 

 where the mine was a very dry one, it was here in such a 

 condition that the flame would be extinguished as soon 

 as it touched the damp walls. The necessity of watering 

 dusty mines has been pointed out by Inspector Gilpin, 

 and this is said to be practised in some of the Belgian 

 collieries. The present instance shows that such a pre- 

 caution would tend to reduce the range of the explosion 

 of the dust. 



Attempts were made to restore the ventilation of the 

 workings in the Albion Mines, when the presence of a 

 large fire was discovered, and this made it necessary to 

 flocd the galleries. In about 48 hours after the explosion, 

 a trench had been cut through to East River, and the 

 water was let in at the rate of 15,000 gallons per minute, 

 until, within a week, all the workings were filled. This, 

 of course, made further investigations impossible, and 

 nothing will be known beyond what has here been 

 told. 



The subject is one of acknowledged importance. 

 There have been frequent explosions in flouring mills, 

 said to be attributable to the ignition of flour dust. At 

 a late meeting of the Manchester Geological Society, (in 

 England), experiments were made to show that even finely 

 powdered slate will spread the flame of gas explosions. 

 Since the preparation of the present paper, a report has 

 been made before the royal commission on accidents in 

 mines, by Mr. F. A. Abel, Chemist to the British War 

 Department, in which it is claimed, as demonstrated, that 

 coal-dust is not only a fiercely burning agent, but when 

 suspended in air currents may operate as an exploding 

 agent. It operates, aside from its inflammability, as a 

 finely divided solid, in "determining the ignition of only 

 small proportions of fire-damp and air, and consequently 

 in developing explosive effects," i. e., under circumstances 

 which, in the absence of the dust, would be attended by 

 no danger. 



HISTORY OF ALHAZEN'S PROBLEM. 



Abstract of a paper read before the American Association for the 

 Advancement of Science, Cincinnati, August, 1881, by Marcus 

 Baker, U. S. Coast and Geodetic Survey, Washing- 

 ton, D. C. 



Alhazen's problem is an optical one and was thus 

 stated by the Arabian Alhazen for whom the problem is 

 named. " Given a luminous point and a point of vision 

 unequally distant from the center of a convex spherical 

 mirror, determine the point of reflexion." The solution 

 of this problem involves the solution of the following 

 geometrical problem now generally known among mathe- 

 maticians as Alhazen's problem. From two given points 

 in the plane of a given circle draw lines meeting in the 

 circumference and making equal angles with the tangent 

 drawn at that point. 



