L. MECHANICS AND ENGINEERING. 477 



iron as a cheap and efficient preservative of timber. He 

 bases his statement upon the assurance that the decompos- 

 ible nitrogenous and albuminous matters contained in the 

 juices of the tree, to the presence of which its decay is to be 

 ascribed, will, by the injection of a tannate, be changed to 

 insoluble and very stable compounds; or, to speak technic- 

 ally, there will be formed albuminous tannates, analogous 

 in their properties to the gelatinous tannates formed in the 

 tanning of animal skins. In addition to this tanning process, 

 he urges that the gradual oxidation of the iron will cause it 

 to deposit itself in a solid state in the intercellular spaces, 

 and thus effect a species of petrifaction, thereby materially 

 adding to the hardness of the timber, and rendering it more 

 valuable for many industrial uses. In carrying his plan into 

 execution he proposes to use the method of injection invent- 

 ed by Boucherie (vital suction, or the pressure of a liquid 

 column), and either to employ the tannate at one operation, 

 or to inject the tannic acid, and follow this with any soluble 

 salt of iron. 



HYDRAULICS OF GREAT RIVERS. 



The AtJienceum, in a highly commendatory notice of a 

 work by Revy upon hydraulics of the great rivers, especially 

 of the Parana and Uraguay and the estuary of the La Plata, 

 refers to a generalization obscurely indicated in the work, 

 and which the reviewer thinks, if absolute, may be called 

 Revy's law, stating it in the following terms: "The inclina- 

 tion of the surface being the same (and no interference aris- 

 ing from other causes), the velocity of a river is as the square 

 of its depth." 15 A, August 22, 1874, 284. 



EXPLOSIONS OF FIRE-DAMP IX COAL MIXES. 



The subject of the connection between explosions in coal- 

 mines and the weather has attracted the attention of Messrs. 

 Scott and Galloway, in England, during the past four years. 

 Their third report has recently been presented, covering the 

 year 1873; from which it appears that the number of fatal 

 explosions was seventy, causing the loss of one hundred and 

 sixty-three lives. Of these explosions, 58 per cent, are due 

 to changes of barometric pressure; 17 per cent, to great 

 heat ; 25 per cent, are not attributed to meteorological agen- 



