Maech 9, 1883.] 



SCIENCE. 



139 



eided to replace them by others ; which, by 

 making the lights more easy to be distin- 

 guished, will, besides, increase the range. 

 The present characteristics are as follows : — 



1. A single fixed light. 



2. A double fixed light. 



3. An eclipsed light, with flashes every half-minute. 



4. An eclipsed light, with flashes every minute. 



5. A fixed light varied by flashes every four min- 

 utes. 



6. A fixed light varied by red flashes every four 

 minutes. 



7. A light with alternate red and white flashes. 



Fixed lights are obtained with a Fresnel 

 apparatus with cylindrical lenses ; the double 

 fixed light, bjr two lights situated at such a 

 distance that they can easily be distinguished 

 from each other, but still appear to form a pair. 

 Fixed lights will eventuallj' disappear, because 

 they have a less range than flashing lights, and 

 also are liable to be confounded with other 

 fixed lights not belonging to a s^'stem of coast- 

 lighting. 



Flashing lights are obtained by means of 

 optical apparatus having generally eight faces : 

 each face comprises, first, a lens of the same 

 width as the face, then, above and below, por- 

 tions of rings having as a common centre the 

 centre of the lens. The apparatus thus gives 

 rise to eight beams of light, separated by dark 

 intervals ; and, when it is turned, the naviga- 

 tor sees alternateljr a flash and an eclipse. 

 The intervals between the flashes depend upon 

 the rapiditj^ of rotation. This light has the 

 inconvenience of requiring sustained attention, 

 and of consulting a timepiece to tell the 

 length of the interval. It should be sup- 

 pressed. 



The fixed lights varied b}- flashes are ob- 

 tained bj' means of an apparatus for a fixed 

 light around which turn two or three vertical 

 lenses which give flashes, either white or red, 

 or alternatel}' white or red, at intervals of some 

 minutes. These slowly revolving lights have 

 the same fault as the preceding, and will also 

 eventually disappear. 



The characteristic which will be generally 

 adopted is that of a scintillating light. To 

 produce it, a fixed-light apparatus is emploj'ed, 

 around which revolves a drum of lenses, placed 

 verticallj-, composed of straight glass bars of 

 lenticular cross-section ; each of these con- 

 centrates the horizontal rays, and consequently 

 produces a fiash. During a rotation, if all 

 the lenses are alike, the navigator will see a 

 series of equal white flashes, producing a scin- 

 tillating light. If the vertical lenses are alter- 

 nately' red and white, there will be alternately 

 a red and white flash, and a compound red- 



and-white scintillating light will result. In 

 the same way, bj' placing the lenses in groups, 

 there can be two, three, four, or more white 

 flashes, followed by a red one. It should be 

 remarked, that, in this case, as the red color 

 diminishes the luminous intensity, the red lens 

 should have larger dimensions to compensate 

 for this loss : as this causes a loss of light, 

 M. Allard prefers, in most cases, to separate 

 the group of white flashes simplj' by an obscure 

 interval. This is obtained by a simple modi- 

 fication in the form of the vertical lenses. 

 There are thus the following eight characteris- 

 tics : — 



1. White scintillating light. 



2. Light with alternate red and white flashes. 



3. Light with two white flashes and one red succes- 

 sively. 



4. Light with three white flashes and one red 

 successively. 



5. Light with four white flashes and one red .suc- 

 cessively. 



6. Light with two white flashes, with intervals of 

 ohscurity. 



7. Light with three white flashes, with intervals of 

 obscurity. 



8. Light with four white flashes, with intervals of 

 obscurity. 



These are the only characteristics which 

 have been definitely adopted. They have the 

 advantage of being readily recognized withoxit 

 consulting a timepiece. 



LETTERS TO THE EDITOR. 

 The new comet in Pegasus. 



I DESIRE to give publicity to the following state- 

 ment regarding the priority of discovery of the new 

 comet in Pegasus. I discovered it at seven o'clock 

 last evening; and, as soon as the direction and rate of 

 motion was ascertained, I repaired to the telegraph- 

 office (a mile away), and telegraphed its discovery to 

 several astronomers, and to Professor Pickering to 

 cable to Europe. In journeying thither I must have 

 passed the messenger-boy with a telegram from Mr. 

 W. E. Brooks of Phelps, N.T., which I found at 

 the observatory on my return, announcing to me his 

 discovery of the same object. 



It was then too late to undo the mischief I had 

 innocently done. In fact, I was not even then sure 

 that there was any guilt attaching to the transaction, 

 as he did not give the time of discovery. He imme- 

 diately wrote, however, giving the time as forty-five 

 minutes past six, local time, which letter reached me 

 to-day. 



I consider it my duty to give to the world the ahove 

 facts, that no injustice be done to Mr. Brooks. No 

 instance occurs to me of a comet having been discov- 

 ered by two persons so nearly simultaneously. 



The comet is quite bright, with a strong central 

 condensation, though no nucleus could be detected. 

 Its tail was about 40' in length, faint, straight, and 

 narrow. 



The shutter of the dome of the observatory is un- 

 dergoing some slight repairs, which prevented the 

 use of the 16-inch refractor; and I was, in conse- 



