May, 1904."' 



KNOWLEDGE & SCIENTIFIC NEWS. 



95 



north-oast, the explosion was audible around Holsworthy 

 (62 miles from the works), Hartland (fiS niilosK and Torring- 

 ton: and to the east at many places in South ncvon as far as 

 Exeter, which is not less than ()o miles from the centio of dis- 

 turbance. Thus the sound must have beon heard over nearly 

 the whole of Cornwall, and the ,i,'reater part of Devon, or over 

 a total land-.area of about 3000 sijuaro miles. 



In the case of the minute-guns fired .at Spithead on Feb- 

 ruary I, icjoi, a curious anomaly was observed. In the imme- 

 diate neighbourhood of Spithead, the sound-waves were 

 almost or quite inaudible, and it was only at a distance of 

 50 miles or more up to about So miles that .they attracted 

 general attention. Owing to contrary winds, the somul-waves 

 were refracted over the heads of observers near at hand, and 

 were brought down again by favourable winds to the earth's 

 surface at greater distances. The Hayle explosion affords 

 another instance of this remarkable eft'ect. .\t Camborne, 

 which is only 4 miles east of the works at Hayle, no one, 

 according to one of my informants, seems to liave heard the 

 reports, and, he adds, the wind at the time was blowing in the 

 contrarv direction. 



The Aviglia-na. Explosion of January 

 16. 1900. 



The little town of .Avigliana hes in the valley of the Dora 

 Kiparia, a tributary of the Po, about 14 miles west of Turin. 

 As at Hayle, the various buildings which constitute the dyna- 

 mite factory are isolated from one another, the whole being 

 comprised within an area of about 50 acres. 



The first and greatest explosion occurred in the building in 

 which the nitro-glycerine was prepared, and which, at the 

 time, was estimated to contain about 400 kilogrammes of this 

 material. This was followed by the explosion of nearlv 12,000 

 kilogrammes of dynamite and fulminating cotton contained in 

 magazines which were probably ignited by the fall of burn- 

 ing materials from the first building destroyed. 



Scale oi TVTiles 



O 10 7J) io UO io 



A-t^UTtO^ 





Pai 



I 

 I 



a. ' 



\ 

 I 



\ 

 o \ 



1 \ 



1 ^ 



Fig. 2. 



The curves in the accompanjnng sketch-map (fig. 21 give 

 some idea of the distribution of the damage and other effects 

 due to the explosion. The area of maximum destruction was 

 practically co-extensive with the factory itself. At Avigliana. 

 which is about half a mile distant, all the window-panes were 



broken, and in several of the oldiu- houses cracks were made 

 in the walls .-ind arches. Similar, (hough somewhat slighter, 

 damage occurred at several neighbouring places, all inclndid 

 within the curve marked n, which cmilains an area of .iliout 

 So stjuare miles. Outside this central area lies a /one bounded 

 by the curve h, containing about iSo s(|uare miles and reach- 

 ing to the western suburb of Turin, within which manv, but 

 not nearly all, windows were broken. In the next zone, lying 

 between the curves b and r, the air wave was strong enough 

 to make doors and windows rattle. It will be noticed that 

 the dynamite factory is at some distance from the centres of 

 all three curves, the last of which (i ), indeed, extends 40 miles 

 east of Avigliana and only eight mil(;s to the west. 



Beyond the latter curve the only effect observed was a 

 rumbling sound like that of distant thunder or a cart of wood 

 being unloaded. This was heard at i-onsiderablc distances in 

 some directions, but the peculiar form of the curve (/ which 

 bounds it is in part, no doubt, owing to a defective series of 

 observations. Towards the south-east it reaches as far as 

 S.avona (75 miles), towards the east to Pavia (87 miles), and 

 towards the north-east as far as Lugano (qij miles). On (lie 

 other hand, towards the west the sound was inaudible at Susa 

 and Fcnestrelle. 1> )lh of which are only 17 miles from Avig- 

 liana. 



Dr. Mario Haratta, who has stuilii'tl this ex])losion, considers 

 that the restriction of the curves towards the west is in great 

 part due to tlie form of the land-surface. Without under- 

 rating the effects of the wind, the direction of which at the 

 time of the explosion is unknown, he points out that tlie path 

 of the waves would be obstructed by the mountain ranges 

 lying to the west and south-west, wliile the open ground along 

 the valleys of the Dora and Po would allow free passage to the 

 sound-waves in other directions. Comparing the curves of 

 lig. 2 with a contour-map of the district, he finds that the 

 rc]-)ort of the explosion was never he.ard in places situated at 

 an altitude of more than 1000 metres. 



ASTRONOMICAL. 



A new form of Dipleidoscope. 



In a brief note communicated to the Royal Dublin .Society, 

 .Sir Howard Cirubb describes a simple little instrument for 

 readily determining the true time by observation of the sun. 

 The instrument in (juestion, the dipleidoscope, was originally 

 devised more than sixty years ago by E. J. Dent. It consisted 

 of a right-angled prism so placed that the sun, when near the 

 meridian, could be viewed in it obliquely, when two images 

 were seen, the one due to rcllection from the first surface, the 

 other to double reflection from the- two inner surfaces. The 

 two images would therefore appear to move in different direc- 

 tions, and when the prism was properly set would overlap 

 when the sun was on the meridian. The instrument, however, 

 as originally devised, was open to some serious ol^jections. 

 The one image of the sun was faint, the other excessively 

 brilliant, and neither being magnified, the observation was 

 only a rough one. By covering one-h.alf of the prism with 'a 

 film of sulphide of lead, and by adding a lens of 20 feet focus, 

 Sir Howard Grnbb has been al)le to make the two images of 

 equal brightness, and sufficiently large for an imskilled 

 observer to determine tlie lime to the nearest second. 



# « * 



RegistraLtion of Sta.r Transits by 

 Photography. 



Sir Howard (irubl) has made an exceedingly in,i<enious yet 

 simple suggestion for getting over the difficulty which has been 

 experienced in employing photography to register star 



