Mechanical Science. 393 



determine the actual pressure, will not interfere with the regular 

 operation of a press, as the articles under pressure may be in the 

 press at the same time the balls are used, which of course must be 

 placed between separate plates. — Phil. Mag. N. S. vi. 284. 



2. Night Telegraph. — A night telegraph, invented by M. Lecot de 

 Kerveguen, appears from the French journals to attract some atten- 

 tion, because of its novelty, cheapness, and applicability, both by 

 day and night. The inventor has gradually improved it until he 

 can obtain 29,245 signs by its means. It consists of a cabin with 

 two faces, for the purpose of transmitting signals in two directions. 

 These faces are pierced with three circular holes, each divided by a 

 vertical and a horizontal diameter. Each hole is covered by an 

 opaque black disc, in which is opened a ray or line, which is ren- 

 dered white for day observation, and luminous at night time. Mo- 

 tion is given to the discs, and consequently to the rays from within 

 the cabin, so that right or acute angles to the right or the left, up- 

 wards or downwards, may be made at pleasure. The dimensions 

 of the cabin are proportional to the diameter of the discs, and the 

 rays on these are themselves proportional to the distance between 

 the telegraph and its correspondent one. 



The following are some of many experiments made with this 

 apparatus: they took place on the 21st of March, at eight o'clock 

 in the evening by bright moonlight: — 



The first ray was 4 feet 6 inches long by 8 inches wide, 

 second 4 do. 6 do. 



third 3 do. 4 do. 



fourth 2 do. 3 do. 



The telegraph was at the port of Toulon, and all the signals were 

 well observed by the men at Cape Sepet, which is 14- leagues dis- 

 tant. On the following morning the experiments were repeated 

 with the white rays by day-light. From these experiments it ap- 

 peared that the smallest ray was abundantly visible at the distance 

 mentioned, and experiments since have shewn at a distance even 

 more than double. 



Still more recently, M. Kerveguen has so far simplified his 

 arrangements as to use only one ray or bar of light ; and though he 

 has by doing so reduced his arbitrary signs to 8649, yet that is a 

 number abundantly sufficient for all ordinary uses. In the new ex- 

 periments made the smallest ray was used, and still found fully 

 sufficient for its intended purpose. — Revue Ency, xliii. 763. 



3. Chinese Canal. — A canal was opened in 1825, to the west of 

 Sargan, in Cochin China, which connected that town with a branch 

 of the river Cambodja. Its length was 23 miles, its width 80 feet, 

 and its depth 12 feet. This canal was begun and finished in six 

 weeks, although it had to be carried through large forests and over 



