328 



Art. XVI. MISCELLANEOUS INTELLIGENCE. 

 I. Mechanical Science. 



Average power of engines, 20.664 horse power. 



Cleland on Steam-engines, 



2. Times of the Motion of Solar Spots. — Mr. Emmett has made 

 many observations upon the motion of solar spots, all of which 

 tend to disprove the opinion that they are hidden and in sight for 

 equal times, and to support the observations of older astronomers, 

 who state the times of appearance and disappearance to be differ- 

 ent. Mr. Emmett makes out the time during which they are vi- 

 sible to be 12^ s'' 30™, and that during which they are invisible 

 to be nearly 15^ 3** 30"". These nearly accord with the times 

 mentioned^ by Kirchius, Stannyan, Cassini, Scc.y and he thinks 

 that imperfection in the instruments, or inaccuracy in the mode 

 of observation, cannot fairly be urged to account for the great dif- 

 ference between these and equal times. — Ann, Phil. N. S. ix. 381. 



3. Naphtha Lamps, or Lights. — M. Joseph Hecker, director of 

 the saltworks, and administrator of the mines at Iruskawetzin Gal- 

 licia, has found that naphtha burns much better than oils or other 

 substances in mines, containing bad air, and injures the health 

 of the workmen less. The light of petroleum is to that of colza 

 oil as 1000 : 831.3, and to that of tallow as 1000 : 500.3, sup- 

 posing that the first burns with a small flame. The quantity of 

 naphtha burnt for lighting the same space is to that of tallow as 

 1000 : 925.74, and to that of colza oil as 1000 : 673.28 ; coal-tar 

 oil, which is in the same proportion as naphtha, is preferable to it, 

 being less expensive ; oil of bones is that which yields the most 

 brilliant light. In the lighting of mines containing bad air, colza 

 oil and tallow will be extinguished, when naphtha, petroleum, and 

 the oil of bones will still burn ; but naphtha and petroleum are 

 then readily extinguished by slight motion or concussion in the 

 air, the oil of bones being in this case best for use. M. Hecker has 

 found that, in mines where the oxygen had diminished to 18.33 

 per cent., men were not incommoded. Generally tallow or colz?i 



