Jan. 22, 1885] 



NA 1 URE 



275 



I venture to think, therefore, that the proof is fairly 

 complete that the luminosity of a candle or gas Maine 

 proceeds from incandescent matter in a state of extremely 

 fine division, because — 



(A) Light can be reflected from it in the same way as 

 from very fine particles of lac, sulphur, &c. 



(B) The reflection begins with the violet rays when the 

 precipitate first forms, and extends to the red as it 

 becomes denser in the upper smoky part of the flame, 

 the spectrum undergoing a similar change to that of the 

 acidulated hyposulphite solution. 



(C) There is no break in the phenomena from the com- 

 mencement of incandescence to the cooling smoke and 

 even the cold soot itself. The reflection is visibly pro- 

 duced by any rays, whether of the sun or from a lamp, 

 that are more intense than those of the incandescent 

 body ; and 1 imagine that light that is less intense is still 

 reflected, though it cannot be discerned. 



(D) The spectrum of light transmitted through a flame 

 is complementary to that reflected from it, as is also the 

 case with a solution containing fine particles. 



(E) The peculiar property of polarising all light re- 

 flected at right angles to the line of incidence which is 

 considered the test of solid matter in extremely fine 

 division is possessed by all flames giving what is known 

 as the "solid" spectrum. 



F Whenever a precipitate is actually formed by a 

 reaction known to take place in either inner or outer 

 flame, the resulting luminous flame has the optical pro- 

 perties described in this paper. Thus zinc, which pro- 

 duces these results only 111 the outer flame, gives evidence 

 of the solidity of its oxide in the form of smoke. And 

 with the mixture of copper sulphate and ammonium 

 chloride it is not that part of the flame that looks most 

 like smoke to the eye, but that which gives a "hard" 

 continuous spectrum which is found capable of reflecting 

 light. 



1 am still working on the lines indicated by these ex- 

 periments, and though the foregoing is all I feel justified 

 in publishing at present, it by no means contains all the 

 suggestive results I have obtained in my endeavour to 

 ascertain the cause of luminosity in gases and substances 

 vaporised in the Bunsen flame. My time is very much 

 occupied and my appliances limited : it may be long 

 before I can complete my researches, so I have thought 

 it well to make public my conclusions, so far as they go. 

 George J. Burch 



A LINE-DIVIDER 



( ~ALI LEO'S proportional compasses are said to date 

 ^-* from the year 1597. We infer that the instrument 

 consisted of two arms, jointed, as in the accompanying 

 figure, so that one arm could move freely about the joint. 

 Each arm had a number of equal divisions (not neces- 

 sarily of the same length on each arm), the zero point 

 being at the joint. To divide a given length into five 

 equal parts it is necessary to take an ordinary pair of 

 compasses and measure the given length with these, then 

 set the proportional compasses so that the fifth division 

 on each arm may be at the given distance apart, then 

 transfer with the ordinary compasses the distance between 

 the unit divisions — this will be one-fifth of the given line. 

 This seems to have been the manner of using the instru- 

 ment employed by Galileo (cf. Marie, Histoire des Sciences 

 Matkimatiques et Physiques, tome iii. p. ioS). Other 

 modes of using will doubtless occur to most of our 

 readers. The principle involved in this and similar in- 

 struments, and certainly in the one before us, is that of 

 the proportionality of corresponding sides in similar 

 triangles. 



Our figure represents Miss Marks's patent line-divider 

 for dividing any space into a number of equal parts. 



A vj forms a hinged rule with a firm joint ; each limb is 

 ten inches in length (in the specimen we are describing), 

 the limb 1; is bevelled, fronted with brass, and presents a 

 straight edge, so that straight lines can be drawn along 

 it. The limb a is also bevelled, and is divided on the 

 bevelled edge and also on the top into eighty equal parts, 

 so that we are enabled to divide a given length into any 

 number of equal parts from two to eighty. A is fitted to 

 slide in an undercut groove upon the plain rule C, which 

 has a single line marked upon it, and is also provided 

 with needle points on the under-side, to prevent it from 

 slipping when placed in any position. 



Suppose we take the case already considered. Slide 

 C along A till the C line coincides with one of the lines on 

 A, against which is the number 50. Place the correspond- 

 ing line on the level of a on one end of the line to be 



divided, then open out or close up the rule till the bevel 

 of B passes through the other end of the line. Now press 

 the points on the underside of C firmly into the paper, and 

 slide A up till the number 4 on the line of reference is 

 coincident with the line on c, and mark the point where 

 the bevel of B meets the given line to be divided. Con- 

 tinue to move A up one division at a time till the whole 

 line is divided. If we require lines to be drawn through 

 the several points of division in a given constant direc- 

 tion, it is obvious that we must fix the instrument so that 

 the bevel of B shall be initially in the given direction. 



We have said enough to show how the divider is used, 

 and it remains only to state that it appears to be a very 

 handy instrument for architects, engineers, and practical 

 drawing. Stanley, of Great Turnstile, Holborn, is the 

 maker. 



UNIVERSAL TIME AND THE RAILWAYS 



ONE of the reasons why the Prime Meridian Confer- 

 ence met at Washington was that the United States 

 possesses the greatest longitudinal extension of any 

 country traversed by railway and telegraph lines, and it is 

 quite in keeping with the spirit of American institutions 

 that some of the most important measures necessary to 

 carry out the resolutions of the Conference were taken by 

 the railway men before the scientific men had begun their 

 sittings. The action of the railway companies began as 

 far back as 1SS3. It was a regular rebellion against the 

 inconvenience of having more than half a hundred 

 standards of railway time from east to west of the 

 continent. At the Conference itself, Mr. W. F. Allen, 

 one of the United States delegates, who has from 

 the first taken the greatest interest in this special 

 branch of the subject, brought the matter prominently 

 before the Congress, stating what had been done. 

 Since the Conference met, the suggestions primarily due 

 to the railway authorities have been accepted by the 

 Army Signal Corps and other public bodies, and from 

 the east of Canada to the Pacific the Continent is now 

 divided into five sections, each with its time standard, 

 differing by one hour from those to the east and west. 

 Thus we have Intercolonial time, Eastern time, Central 

 time, Mountain time, and Pacific time, representing dif- 

 ferences of one hour or 15" of longitude. We append a 

 map, and a paper by Mr. Allen, which we have received 



