14 MOVEMENT 



the same impression by the length of the stroke, that 

 is to say, by a natural graphic expression.* 



The Uses of Photography in recording Time. — If the 

 recording needle cannot be applied to the study of 

 any particular phenomenon, recourse must be had 

 to photography. It is by this means that a system 

 of optical telegraphy has been perfected, by which 

 flashes of light can be transmitted from one point 

 to another, and received as a series of dots and dashes, 

 such as constitute the Morse Code. 



The luminous point at the transmitting station is 

 alternately, and at various intervals, exhibited and 

 obscured by the movement of a screen. This con- 

 stitutes the transmitting apparatus. The rays of light 

 emanating from this source are rendered parallel by 

 the interposition of a lens, and traverse the inter- 

 vening space to impinge upon a similar lens at the 

 receiving station. 



At the focal point of this second lens the image 

 of the luminous source is visible in the form of a 

 brilliant spot. If the sensitive surface, upon which 

 this image falls, is allowed to travel at a uniform 

 rate, short flashes of light will produce spots, and 

 sustained flashes will give lines. An arrangement 

 of this kind has many scientific applications, but it 

 is not in this manner that photography has been 

 most usefully employed in time-measurements. It has 

 chiefly been utilized for two purposes. Firstly, to 



* During late years many inventors have constructed similar 

 machines, and we believe that even this is not the lirrt which auto- 

 matically inscribed an air executed on the piano. Among instru- 

 ments of lecent design there is a very remarkable one, which we 

 owe to Messrs. Cros and Carpentier, and which is known as the 

 "Melograph." This instrument is not intended to register the air 

 as played by the artist, but it perforates a strip of paper in such a 

 way that when it is repassed through the machine the piece of musio 

 winch has b en executed by the operator is reproduced by it with 

 perfect fidelity. 



