482 



NATURE 



{April 18, 1872 



252 45s_X i7j_ _ nnj^.jj^ Q2. Av. ; hence we may as- 



437-5 

 sume that the entire weight of water which fell on one 



square mile was 5 3°S6,.44X 997-137 ^ ,,449,, 36 tons, 



3 5, 5540 

 {-:-. -984 = 1,472,699 milliers). Some idea of this enor- 

 mous quantity will be afforded by the following illustra- 

 tions. 



The Thames at London Bridge is, at low water, nearly 

 700 feet wide,* and from 12 to 13 (say i2'5) feet deep. 

 ■We will, for the sake of argument, assume the sectional 

 area throughout to be 700 X 125 = 8,750 square feet. 

 The amount of rainfall on a square mile was equivalent 

 to a volume of water corresponding in sectional area to 



the Thames at London Bridge, and extending J*—^ ' „ = 



8750X5280 

 I '127 miles in length; in other words, it would extend 

 from London Bridge, past Cannon Street (Railway), South- 

 warkandBIackfriars (Railway and Road) Bridges, to about 

 Somerset House, or nearly to Waterloo Bridge. 



The same quantity of water would equal the contents 

 of a river or canal having an uniform width of 20 feet, and 

 depth of 5 feet — the sectional area being soofeet — extend- 

 ing nearly 99 miles, or 1 59 kilometres in length. 



The cubic contents of a sphere are 5 of that of a cylinder 

 of the same diameter and altitude. But the altitude being 

 equal to the diameter, and S of '7854 being "5236, the con- 

 tents may be expressed as I have arranged it in the follow- 

 ing formula. Calling A the diameter, and x the cubic 

 contents required, we have 



A^ X -5236 = X, 

 or the reverse, calling C the cubic contents and x the 

 diameter required. 



\l •C2:!fi 



'V -5236 



By these formukc I have determined that the rainfall 

 on a square mile — under the conditions mentioned in 

 paragraph 3— was equivalent to a globe of water 463 ft. 

 in diameter (approximate), a height exceeding that of the 

 top of the cross surmounting the dome above the pave- 

 ment of the churchyard of St. Paul's Cathedral (370 ft. f) 

 by 93 ft. 



The same quantity of water was equivalent to the fol- 

 lowing : — 



A circular column of water 144 ft. in diameter (corre- 

 sponding to that of the dome of St. Paul's Cathedral — in- 

 terior surface^), rising to a height of 3,198 ft.; in other 

 words, it would be upwards of 8J times the height of the 

 cross before-mentioned. 



Or, with regard to specific gravity : — 



A circular column of lead (cast)§ of the same diameter 

 (144 ft. — acubicfiot being taken as 7 10 lbs., or 1 1,360 oz.) 

 containing 4,571,921 cubic ft., and rising to a height of 

 278 ft. 



A circular column of granite (Aberdeen) of the same 

 diameter, a cubic foot being taken as 2,690 oz.,!j containing 

 19,307,443 rubic feet, and rising to a height of 1,184 ft. 



But perhaps the most remarkable illustration will be 

 afforded by comparing the weight of this quantity of water 

 to a corresponding v/eight contained in, say, a num- 

 ber of railway coal waggons. Railway coal waggons 

 are constructed to carry, on an average, from eight to ten 

 tons. Let us assume it as the former of the two, and 

 the average length of a number of waggons as 16 feet 



* I quote this from a paper "On the Rainfall of Devonshire," by W. 

 Pengelly, Esq.. F.R.S., Scientific Opinion,yo\. i.p. 137. (From the Trans- 

 actions of the Devonshire Association for the Advancement of Science, 1868.) 

 The depth is confirmed in the Eiuyclopirdta Byittanica, Vol. xxi p. 163. 



t Encyclopedia Brittanica, vol. xiii. p. 670. 



X From the Cathedral authorities. 



§ " Sprague's Pocket Tables (Architects and Surveyors)," p. q. 



II Ibid. 



each from buffer to buffer. It would require no less than 

 181,142 such waggons to carry a corresponding weight of 

 coal (or 3,623 heavy trains of fifty waggons each) which 

 would, when close coupled, i.e., buffer to buffer, extend 

 over a distance of nearly 549 miles (883 kilometres) 

 represented very nearly by the distance from London 

 (Euston Station) to Aberdeen via Rugby, Stafford, Crewe, 

 Carlisle, Glasgow, and Perth (London and North Western 

 and Caledonian Railways). An express train, travelling 

 at an uniform speed of sixty miles per hour, would take 

 upwards of nine hours to run this distance, in other words, 

 to pass this number of waggons ; or, if 1 may indulge in 

 another illustration, this number of waggons would, if 

 travelling at an uniform rate of twenty-five miles per 

 hour — which is about the average rate of goods trains — 

 be nearly twenty-two hours in passing any given point, 

 such, for instance, as a station. (Aberdeen is upwards 

 of 130 miles N.N.E. of Edinburgh by the Caledonian 

 Railway — Eastern route from London.) 



Such a means of illustration as the one 1 have here 

 set forth may not be considered in all respects strictly 

 scientific ; it has nevertheless this advantage, it enables 

 us to comprehend something of the truth and magnitude 

 of the subject — although dealing with hypotheses — where 

 mere abstract figures would fail to produce anything like 

 a similar result. John James Hall 



ON CERTAIN PHENOMENA ASSOCIATED 

 WITH A HYDROGEN FLAME 



PHENOMENA of much interest and possibly of 

 J- future usefulness are associated with the combustion 

 of ordinary hydrogen. 



I. To' study these phenomena free from disturbing 

 causes three things should be attended to, although the 

 effects to be described can be obtained without any special 

 precaution. 



(,7) The gas must be stored and purified in the ordinary 

 way, namtly, by passing into a gas-holder through a 

 solution of potash, and then through a solution of per- 

 chloride of mercury or nitrate of silver. 



(b) From the holder the gas must be led through red 

 or black india-rubber tubing to a platinum, or better, a 

 steatite jet. 



{c) And then the gas should be burnt in a perfectly 

 dark room, and amid calm and dustless air. 



II. In this way the flame gives a faint reddish brown 

 colour, invisible in bright daylight. Issuing from a 

 narrow jet in a dark room, a stream of luminosity, more 

 than six times the length of the flame, is seen to stretch 

 upward from the burning hydrogen. This weird ap- 

 pearance is probably caused by the swifter flow of the 

 particles of gas in the centre of the tube. The central 

 particles as they shoot upward are protected awhile by 

 their neighbours ; metaphorically, they are hindered from 

 entering the fiery ordeal which dooms them finally to a 

 watery grave. Dr. Tyndall has shown that the radia- 

 tion fro m burning hydogen is hugely ultra-red, and 

 moreover, that it has not the quality of the radiation from 

 an elementary body like hydrogen, but practically is found 

 to be the radiation from molecules of incandescent steam. 

 So that, except at its base, a hydrogen flame is a hollow 

 stream of glowing water raised to a prodigious heat. 



III. Bringing the flame into contact with solid bodies, 

 in many cases phospliorescent effects are produced. Thus 

 allowing the flame to play for a moment on sand paper 

 and thfn promptly extinguishing the gas, a vivid green, 

 phosphorescence remains for some seconds. The ap- 

 pearance is a beiutiful one, as a luminous and perfect 

 section of the hollow flame is depicted. Similar phospho- 

 rescence is produced by the flame on white writing paper, 



