Oct. 17, 1884.] 



♦ KNOWLEDGE ♦ 



325 



I 



iBiiJrrllnnrn. 



Me. W. Crookks F.K.S., and Drs. W. Odling and C. Meymott 

 Tidy, reporting to Colonel Sir Francis Bolton, official water examiner 

 for the metropolis, on the composition and quality of daily samples 

 <->{ water supplies to London last month, state that of the 168 

 samples derived from the mains of the seven metropolitan water 

 rompanies taking their supply from the Thames and the Lea, " the 

 \\"hole were, without exception, clear, bright, and well filtered. The 

 excellence of the water supplied to the metropolis during August 

 >vas indicated by its state of aeration, and by its freedom from 

 lolour and from any excess of organic matter. Further, its per- 

 fect filtration was evident by the absence of even a trace of sus- 

 pended matter in any one of the numerous samples submitted to 

 I'xamination." 



The experiments on the relative efficiency of different illumi- 

 uants for lighthouse purposes which are being carried out by the 

 Trinity Brethren, aided by the observations of the captains of the 

 mail packets, the Peninsular and Oriental liners, pilot vessels of 

 different nationalities using the channel, trading vessels plying 

 lietween England and foreign ports, and by several French cruisers 

 have in some respects been completed. They support the conclu- 

 sions previously arrived at. So far as has been ascertained at 

 |iresent, there seems to be very little difference for all practical 

 pitrposes between gas and paraffin oil. The gas-light, if any- 

 thing, is slightly superior in fine weather, and the electric light is 

 uverwhelmingly superior to both the other lights. The crucial test 

 (■f the electric light, however, will be in hazy weather, and it is 

 stated that in some experiments which have alreiidy taken place 

 when the weather was rather thick the light did not hold its own 

 .igainst the other luminants. Important tests will take place 

 during the autumu, into which the experiments will be extended, 

 when hazy weather and a greater variety in the conditions of the 

 atmosphere may be expected. 



ExTEXT AND RESOURCES OF Geeat Bkitain. — Those who are 

 lucking for statistics may find some rather startling figures in the 

 .iddress recently delivered by Sir Richard Temple on " Economic 

 Science and Statistics " before the British Association at Montreal. 

 <>n this authority it appears th.at the area of the British Empire is 

 eight and a half million square miles. Including countries poli- 

 tically under its control, such as Egypt, Zululand, and Afghanistan, 

 the total amounts to ten million square miles, or one-fifth of the 

 habitable globe. One-(iuarter of this area has been topographically 

 surveyed. The total coast-line is 28,500 miles, with 48 large 

 harbours. Only one-fifth of the area is cultivated or occupied. 

 There is room enough in Canada and Australia to support a popu- 

 lation of 200,000,000. The total population of the empire amounts 

 to 315,000,000, of which 39,000,000 are Anglo-Saxons and 

 188,000,000 are Hindoos. The annual revenue amounts to 

 £203,000,000 of which sum £80,000,000 come from the 

 United Kingdom, £74,000,000 from India, and £40,000,000 

 from the colonies and dependencies. Only one-forth of the 

 total revenue is derived from land taxation. Including local 

 taxation the revenue is .^;264,000,000, and amounts to £1. 5s. 4d. 

 ior head per annum. The numberof men trained to arms amounts 

 to 850,000, about 700,000 of these being of the fair and dominant 

 race. The defensive armaments by sea and land cost £41,000,000 

 .innnally, which is less than that shown by any great State in the 

 world except in the United States. There are 560,000 policemen 

 iu the empire, 1 to every 571 inhabitants and to every 16 square 

 miles. There are 246 war-vessels, and 30,000 merchant ships 

 manned by 270,000 sailors. The factory steam power in the 

 world is represented by 7,500,000 horse power; of that total 

 2,250,000, or about 30 per cent., is British. If the main elements 

 of national industry' be taken together — namely, commerce, 

 manufactures, mining, agriculture, carrying trade, and 

 bankin— the total £2,000,000,000 and upward annually is 

 about the same for the United Kingdom and the United 

 .States. Bub the United States are advancing the fastest, and 

 are already passing ahead. There are 675,000 persons convicted 

 annually of crime in the empire, of which number more than 

 nineteen-twentieths pertain to India. The number of ])anpers in 

 the United Kingdom under relief amounts to 1,000,000, or rather 

 less than one-thirtieth of the population, and the cost of their 

 uiaiutenance is £10.000,OCO sterling annually. In regard to the 

 Post-Office, the letters posted annually in the world are 

 5,200,000,000; of this total 1,500,000,000, or 34 per cent., are in 

 the British empire. Respecting education, there are 5.250,000 

 pupils at schools in the United Kingdom, 860,000 in Canada, 

 611,000 in Australia, and 2.200,000 in India, making a total of 

 .s.921,000 pupils in the British Empire, 



" Let Elnowledge grow from more to more." — Alibed Tennysob. 



Only a small proportion of Letters received can possibly be in- 

 serted. Correspondents must not le offended, there/ore, should their 

 letters not appear. 



All Editorial communications should he addressed to the Editob op 

 Knowledge; all Business communications to the PuBLisnERS, at the 

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DELAYS ARISE FOE WHICH THE EdITOB IS NOT BESFONSIBLE. 



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The Editor is not responsible for the opinions of correspondents. 



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 AND DIBECTED ENVELOPE BE ENCLOSED. 



THE LUXAB ECLIPSE OF OCTOBER 4. 



[1451] — That well-known Belgian astronomer, my friend M. Ad. 

 de Boe, of Antwerp, sends me an account of so remarkable and 

 interesting an observation of his own of the eclipse of Saturday 

 week that I am induced to hope that you will find space for a precis 

 as short as I can make of it. 



Briefly, then, at the stage of the ecUpse represented in the 

 annexed slightly exaggerated diagram the arc of the earth's 

 shadow was quite decidedly peaked at a instead of being rigidly 

 circular, "II n'ya (says M.de Boe) dans cette observation aucune 

 illusion. Deux personnes presentes la constaterent immediatement." 

 Now, at the time of the phase indicated, the moon was on the 

 horizon of the Cordilleras, while when she was half eclipsed she 

 was similarly placed as regards part of the Pacific Ocean. At this 

 time, however, all traces of the peaked appearance had absolutely 

 vanished, and the periphery of the shadow was sensibly circular. 

 Can the curious deformation figured have been the shadow of the 

 Cordilleras, or had it its origin in the form of the lunar surface ? 



From all my friends abroad and at home I hear of the curious 

 phosphorescent green tint of the earth's shadow during totality, a 

 phenomenon which struck me forcibly in observing the eclipse 

 myself. William Noble. 



Forest Lodge, Oct. 13, 1884. 



INFLUENCE OF MOONLIGHT. 



[1452] — The following, partly for its bearing on MJr. Hays' 

 letter (1445), partly to elicit information on the subject mentioned. 

 A fellow tourist last summer, noticing that I had slept with my 

 bedroom windows open, greeted me with '' You will some day catch 

 an ophthalmia." In further conversation on the subject I was told 

 that an inquiry had been made by French surgeons as to the cause 

 of ophthalmia, which had been noticed to be prevalent among 

 French soldiers in Algeria while camping out. It was found that 

 the sufferers were in general men who, not liking their small close 

 tents, would sleep out in the open. Since the inquiry the men are 



