608 KANSAS CITY REVIEW OF SCIENCE. 



Closely connected with the solution of assuring the maximum of security in 

 railway traveling, is the question of signals; these must not be only visual, easily 

 read by the driver, but the faithful interpretation of electric signals ; they must 

 not be too numerous, in order to afford the means and the leisure to be readily 

 perceived, and not induce undue confidence. Between the look-out for signals 

 and keeping an eye on the line, attention to brakes, and the new system of fur- 

 nace Belpaire, requiring only thin layers of combustibles, both driver and stoker 

 have serious responsibilities and no small anxieties. 



The visual signals are the colored disks and the semaphores with ascending 

 and descending arms ; there are also electric signals between each signal post, to 

 indicate when a block of line is free or closed. But they are the first only that 

 speak to the driver's eyes. Efforts are made to marry the two systems, and the 

 accepted idea is, that electricity ought only to be employed to efface, not to make, 

 the visual signals. And despite every perfection in point of view mechanical, 

 and with fairly worked, intelligent and well paid employees, human fallibility 

 will ever exist as the cause of a certain number of accidents. The very perfect- 

 ing of mechanical contrivances is in itself a danger, as it begets an undue confi- 

 dence of security. A servant can wire the departure of a train, but forget to dis- 

 play the stop-signal to guide the driver of a following train. The problem to 

 solve is to secure the two warnings by one and a simultaneous movement. M. 

 Lartique of the Great Northern of France Railway, appears to have succeeded ; 

 at a station, the man displays the arm signal to stop, and it is by an electric cur- 

 rent from a station further on, that liberates the arm of the semaphore, indicating 

 the train has left and the way is clear. If by chance the electric current failed, 

 etc. , all that could result would be a delay in the succeeding train. 



Lead-intoxication can be produced by a very small dose of that metal intro- 

 duced into the system; its symptoms are recognized by intense headache, colic, 

 nervous irritation, pain in the kidneys, paralysis, etc. It seems we live in an 

 atmosphere of lead ; it is everywhere present, although invisible. Thus M. Gau- 

 tier, an authority on lead-poisoning, exhibits that insiduous poison in walls, wool, 

 leather, clothing, water, the siphons for seltzer water, the crystal flacons for Or- 

 leans vinegar, in white wine bottles, in tinned food, such as preserved vegetables, 

 sardines, lobster foie-gras, tunn, etc. However, neither the emanations from 

 house-painting, nor the salts of lead employed to prepare leather or dye-stuffs, 

 can be a source of serious danger ; in the tins of preserved vegetables, the quanti- 

 ty of lead absorbed is feeble, though the solder contains seventy-five per cent of 

 thct metal. The matter is more serious in the case of sardines or food preserved 

 in oils, or abounding in fat; here oleate of lead is formed and increases in pro- 

 portion to the time the aliment has been boxed up. The French Government 

 has prohibited the internal soldering of sardine cans, but two years must elapse 

 before the stocks on hand can be used up. In the meantime the French con- 

 tractors for the navy, have to supply the-new prepared sardine boxes. After sar- 

 dines rank foies gras and lobster; the former can be had readily in earthenware 



