Page:Popular Science Monthly Volume 55.djvu/584

566 temperature upon health, and its range is of more importance than its mean. The European under a tropical climate suffers from anæmia, diseases of the digestive system, especially of the liver, from malaria, dysentery, typhoid fever, and yellow fever. It is not at all easy to say, however, how much of the excess of mortality of Europeans in tropical and subtropical countries is simply attributable to climatic heat per se, and is consequently inevitable and not the effect of malaria, or how much of it is the direct consequence of habits of life and of the neglect of sanitary laws and of personal hygiene. As Arnould rightly said, the habitudes alimentaires of the Anglo-Saxon constitute one of the stumbling-blocks to health, but by far the most important is malaria, compared with which the rest are relatively insignificant. Mr. Chamberlain was right when he said the other day that 'the man who shall successfully grapple with this foe to humanity and shall find a cure for malarial fever and shall make the tropics livable for the white man, will do more for the world and more for the British Empire than the man who adds a new province to the wide dominions of the Queen.'"

"Picture Telegraphy."—The following account of the new so-called picture telegraphy is from the New York Electrical World and Engineer: "The apparatus consists of a receiver and transmitter, similar in appearance and in mechanism. The picture to be transmitted is drawn on a heavy piece of metal foil, the lines of the drawing being made with an insulating ink. The foil is then secured on the circumference of a horizontal cylinder on the transmitter, the cylinder being of about the size of a typewriter rubber roller. There is a similar cylinder on the receiver, on whose surface is clamped the paper upon which the drawing is to be reproduced; over this is superposed carbon paper, which is covered in turn by a sheet of thin paper. A stylus actuated by an electro-magnet is adjusted close to the surface of the latter, and each time a current is passed through the electro-magnet the stylus is forcibly pressed against the moving surface of the cylinder, and a corresponding mark is made on the two sheets in contact with the carbon paper; the outer sheet serves merely to offer a smooth surface to the stylus and to enable the operator to see that the picture is being properly reproduced. The transmitting cylinder passes under a similar stylus, which latter closes the circuit between the receiving and transmitting ends when it rests upon the foil, and opens the circuit when it passes over the lines drawn with insulating ink, in the latter case actuating the stylus magnet at the receiving end, which leaves a mark on the paper of the receiving cylinder in the form of a line corresponding to the width of the insulation over which the transmitting stylus is passing. The stylus at each end of the line is simultaneously advanced at the end of each revolution of the cylinders by a screw of small pitch. From the description it will be seen that if the surface of the foil on the transmitting cylinder were entirely insulated the receiving stylus would merely draw a number of parallel lines on the paper corresponding to the turns of the screw, and separated a distance corresponding to the pitch of the screw and the angle through which it is turned at each operation. Four different rates of advance may be given to the stylus, corresponding to as many different angles of advance that may, by appropriate mechanism, be given to the screw. The two cylinders have synchronous motion, so that all the marks or lines on the receiving cylinder correspond to widths of insulating ink traced over on the transmitting cylinder. Synchronism is obtained as follows: Connected with both receiver and transmitter is an electric motor which, at the end of every revolution of the cylinder, raises a weight, which acts on a clock train when failing and thus gives motion to the cylinder. At the end of each revolution of the transmitting cylinder a contact is made which locks for an instant the receiving cylinder when it arrives in a position corresponding to a similar position of the transmitting cylinder. Thus it will be seen that each cylinder begins its revolution from identical positions and at the same instant, and as the clockwork of both receiver and transmitter are duplicates, approximate synchronism is maintained during a revolution. Owing to the use of carbon paper, the lines made by the receiver are of considerable width, with the