94 



KNOWLEDGE & SCIENTIFIC NEWS. 



[May, 1904. 



have the same torque as previously observed with a given 

 numl^er of revolutions Mj appear only at a number of revolu- 

 tions Mi (superior to Mj). The same number of revolutions 

 will now correspond with a hij^her torque than before, the 

 torque at rest being evidently also higher. 



The motor is started by altering the ratio of the regulating 

 transformer. The current of the c.xcitor brushes being thus 

 interrupted at rest, the primary coil of the series transformer 

 will act as a reaction coil, and the whole motor will be traversed 

 only by a very small current. It will thus be unnecessary to 

 open the primary coil of the motor when stopping. It is suffi- 

 cient to open the exciting circuit (low tension coil) because the 

 motor works only in the case of the exciting circuit being 

 closed. 



The motors of the Spindlcrsfeld cars have an output of 

 about 100 H.P. hours: they have four poles and a monolateral 

 air gap of 3 mm. The total weight of a motor, including the 

 small toothed wlieel, is 2140 kg., the weight of the exciting 

 current transformers common to both motors being iioo kg. 

 As regards the arrangement of the connections, the direct 

 current multiple unit system of the Union Elektricitats GescUs- 

 chaft has been used and slightly modified. Two cars are being 

 used in connection with the johannisthal-Spindlersfeld trial 

 runs, in addition to three trailers, each 16 tons in weight. The 

 experimental trains arc run on the same track as used for the 

 regulation steam trains, and are inserted between the steam 

 trains according to a fixed time table. The cars are designed 

 for a maximum speed of 40 km. per hour, though speeds as 

 high as 60 km. are sometimes reached. The motors have 

 given full satisfaction even in the case of the highest strains, 

 the whole train, including two motors and three trailers 

 (155 tons), being often arranged and driven by the two motors 

 only. The perfect independence with respect to the line ten- 

 sion has proved a special advantage as compared with the 

 rotary current system, two-thirds of the line tension having 

 been sufficient to maintain the regular service, while starting 

 and running at a speed of about 30 km. was possible with 

 40 per cent, of the motor tension. 



A. G. 



Recent Explosions. 



By Charles Davison, Sc.D., F.G.S. 



Interesting evidence with regard to the propagation of sound 

 by the atmosphere is afforded by the firing of heavy guns 

 during reviews and sham fights, and by explosions in manu- 

 factories of dynamite and nitroglycerine. Examples of the 

 former class have been given in two recent papers. ■ During 

 the great naval review at Spithead on June 26, 1897, held in 

 honour of the late Queen's Diamond Jubilee, the sound of the 

 first salute was heard as far as Weston, near Hath, at a distance 

 of 71 miles. Again, on July 18, 1900, when the I'rench Presi- 

 dent visited Cherbourg, a sham fight took place between 

 two portions of the French fleet, giving rise to disturbances 

 that were mistaken for earthquakes at many points along 

 our southern coasts. The reports were heard from 

 Dawlish and Exmouth on the west, to Brighton and 

 Henfield on the east, the distance from Cherbourg to the 

 latter place being 107 miles. Lastly, during the funeral 

 procession of our late Queen, on February i, kjot, the 

 minute-guns were heard as far as Alderton, near Wood- 

 bridge, in Suftblk, which is 139 miles from Spithead, 



In the present paper, I propose to describe similar 

 evidence derived from two recent explosions, the first at 

 Hayle, on January 5, of the present year, the second at 

 Avigliana, near Turin, on January 16, 1900!. 



♦ "The distance to which the firing of heavy guns is heard ; " 

 Nature, vol. Ixii., 1900. pp. 377-379: "On tlie audibility of the 

 minute-guns fired at Spithead, on February i: " Knowledge, 

 vol. xxiv., i9oi,pp- 104-105. 



f For the account of the H,-xylu exiilosioii, I have relied on the 

 reports which appeared in the M'estern Morning AVa-s (Plymouth), 

 and on replies to ,a letter whicii the ICditor of that paper kindly 

 inserted. Dr. M. Baratta has puljlislicd an interesting report on 

 " Lo scoppio del dinamiti-ficio cH .\vigliana c la geo liscia (16 

 gennaio, 1900) : " Turin, 1900. 



The HaLyle Explosion of January 5, 1904. 



The works of the National Explosives Company at Hayle 

 are situated on waste land, known as Upton Towans, about two 

 miles north-east of Hayle and between three and four miles 

 east of St. Ives. To reduce all risks to a minimmn. the 

 separate buildings are isolated as much as possible ; and, to 

 lessen the loss of life, in case an explosion should occur, the 

 number of men employed in any building is always small. It 

 was no doubt owing to the observance of these precautions 

 that the loss of life during the recent disaster was compara- 

 tively slight. 



At the time of the explosion (10.55 a.m.), nitro-glycerine was 

 flowing down a gutter from the precipitating house to the 

 filtering house, the latter lying about 400 yards north-west of 

 the former. Only one man was working in the precipitating 

 house and three men in the filtering house. It appears tliat 

 the precipitating house was the first to explode, and that, 

 owing to the temporary connection by means of the gutter, 

 the filtering house followed immediately. This conclusion 

 rests on the evidence of an eye-witness ; on the fact that 

 persons to the south-east of the houses heard two reports 

 separated by from li to 2 sees., while those in the opposite 

 direction heard only one; and on the cDndition of the gutter, 

 which was not covered by the debris from the precipitating 

 house. Both houses were, of course, destroyed, and their 

 occupants killed instantaneously. As to the cause of the ex- 

 plosion, it can only be surmised — but the surmise is a probable 

 one — that it was due to the fall of some heavy weight, cither 

 of one of the lead cups used to catch the droppings from the 

 taps, or, more prol^ably, of the lid of one of the tanks. In any 

 case, the disaster must have been purely accidental in its 

 origin. 



The results of the explosion were visible for several miles 

 around the works, chiefly in the breakage of glass. At Hayle, 

 many windows were blown out. At St. Ives, the damage was 

 estimated at not less than £200, but its distribution was par- 

 tial, some houses suffering and others close at hand escaping ; 

 and it is worthy of notice, though the peculiarity has been 

 recorded before, that the windows, especially in houses facing 

 the works, were blown, not inwards, but outwards. Similar 

 damage also occurred at St. Erth (3* miles from the works), at 

 Leedstown (4 miles), and, though to a mtich less extent, at 

 Penzance (distant 9 miles). 



A suiall oscillation of the ground was also noticed in the 

 surrounding district. At St. Ives, according to my informant 

 quoted above, the vibrations could not be distinguished from 

 those produced by an earthquake. At much greater distances 

 windows were shaken ; but this must have been caused by air- 

 waves. Observations of this kind were made at several 

 places in Devon, at Ivybridge and Modbury (68 miles), near 

 Torrington (74 miles), at Paignton (83 miles), Torquay 

 (85 miles), and Teignmouth (88 miles). 



The distribution of the places where the reports were dis- 

 tinctly heard is shown in the sketch-map in fig. i. To the 



Scalt al Milts 



HaTtlanS 



Fulford 



Fig. 1. 



