128 ANNUAL OF SCIENTIFIC DISCOVERY. 



From the foregoing considerations, then, it would appear that when 

 the mind is engaged with the perception of distance, the presence of 

 color is often overlooked ; its absence may remain unnoticed from the 

 same cause ; for in uncolored stereographs of objects that are perfectly 

 familiar to the observer, it will sometimes be noticed, that those 

 articles which do not greatly differ in color from the tint of the pho- 

 tographic paper, are seen in the stereoscope with an approximation 

 to thtir natural hues ; upon withdrawing the slide from the instru- 

 ment no trace of such tint is perceived. Objects that are free from 

 lustre, as well-worn carpets, answer for this purpose. That this 

 should be the case with the tinted photographic representations of 

 white objects can be explained of course in another way. Contribu- 

 ted to Silliman's Journal, Sept., 1861, by Prof. 0. N. Rood, Troy 

 University. 



The chromatic effects here noticed by Prof. Rood are well seen 

 in the ordinary camera and dark chamber. Thus the human counte- 

 nance, when not florid, presents to the unartistic eye few or no traces 

 of pink or flesh color but every one who has seen it in the camera, 

 must have observed with what distinctness the image is colored. 

 The same is true of familiar landscapes, when seen inverted upon the 

 screen in a dark chamber. Here the neutral tints, which in nature 

 are almost unnoticed by the common observer, stand out as distinct 

 patches of color in the way so well described by Prof. Rood. Eds. 

 Journal. 



NIGHT TELEGRAPHIC SIGNALS. 



A plan for communicating between lighthouses, forts, ships of war, 

 etc. at night, has recently been invented by Mr. H. P. Tuttle, of the 

 Harvard Observatory, Cambridge. It consists of a box about six 

 inches wide and twelve long, with an aperture in front through 

 which is seen a brilliant light. The aperture is provided with a cut- 

 off which is worked by a lever, and the system by which the charac- 

 ters are made is precisely the same as those of our Morse telegraph : 

 different combinations of length, there being only two lengths, with 

 the number of times the lig-ht is cut off, designating each letter of the 



^j ' dJ C? 



alphabet, which are read by sight ; whereas, the same characters over 

 a telegraph wire are read in our telegraph offices by sound. The 

 distance at which the light can be read depends upon the quality and 

 size of the lens, which is immediately behind the aperture. Those 

 already experimented with are common dark lanterns, and are bril- 

 liant enough to be read distinctly at a distance of three miles. Lamps 

 can be made at a very slight cost which can be read ten miles with 

 the naked eye, and by aid of glasses, twenty-five miles. 



Powerful lights can also be used, which may be read twenty-five 

 miles or more with the naked eye. Two telegraph operators, in 

 connection with Mr. Tuttle, experimented at night between the cu- 

 pola of the State House, Boston, and the top of the Bunker Hill monu- 

 ment, carrying on a spirited conversation without the slightest trouble. 

 From ten to fifteen words per minute were transmitted with rough 

 and imperfect machines. The rapidity of transmission can be con- 

 siderably increased by using machines of improved manufacture. 



It is not necessary for telegraph operators, exclusively, to operate 



