SODA FOR. INCRUSTATIONS rN BOILERS.— We have received a letter from one of our subscribers in Royalton, Oldham, Lancashire, Eng., who informs us that soda is not a preven-tative ol incrustations in steam boilers. It indeed precipitates the lime in the water, but that is just the thing which should be avoided as it falls down and attaches itself to the bottom of the boiler. His brother ruined in a short time, a stood steam boiler by the use of soda to prevent incrustations. He suggests an acid instead of an alkali to hold the lime of the water in solution in the .boiler. We must say, however, that no known acid in combination with the lime, will hold it in solution in the boiler. The two will form a salt, which will fall to the bottom, such as the sulphate of lime il sulphuric acid is used. KENTUCKY MECHANICS' INSTITUTE.—This new Institute, established in Louisville, has published the circular for its first annual fair. It is to be held in the month of October next. We hope the mechanics of Louisville will have a good fair. We understand they build the finest steamboats on the Mississippi ; such is the reputation they have here. WATER POWER AT NIAGARA FALLS.—We see it stated in a number of our exchanges, that a hydraulic canal at Niagara Falls, is about to be commenced, for factory purposes we suppose. It is stated that a company is formed for the object with a capital of $500-000. The canal is to be nearly a mile long, seven feet wide, and ten feet deep, cut through the sslid rock. It will form the finest water privileges for factories in the world, but we are not so sure about the sites for buildings— they cannot be built at the bottom of the falls. BLACK AND FAIR HAIR.—There is rather an amusing article on " Human Hair," in the late number ol the " London Quarterly Review." In Europe the fairest haired inhabitants are found north of the parallel of 48 . Between 48 and 45 parallel, there is a debatable land of dark brown hair, and to the tropics the races are generally black haired. There are exceptions, however, to these lines, as the Venetians have been distinguished for golden hair, while in Ireland the Celts have been distinguished for black hair. In Ameri- :a, however, among the Anglo Saxon races, very fair people are found in the pine woods sf the Southern States. The difference of color in the hair is owing to the tint of the fluid which fills the hollow tube in each hair. This fluid has been analyzed by Liebig, and the result shows " that the beautiful golden hair owes its brightness to in excess of sulphur and oxygen with a deficiency of carbon, whilst black hair owes its jetty aspect to an excess of carbon and a deficiency of sulphur and oxygen." Few, perhaps, have ever bestowed a thought upon the number of hairs in the human head. A German, it seems, has applied himself to the task of counting them, and gives us the result of his labors :—" In a blond one, he lound 140,-040 hairs; in a brown, 109,440; in a black, 102,962 ; and in e red one, 88,740." The red appears to be the coarsest, and yet we find silky and coarse fair haired people, and some have red hair of a beautiful soft] silky and wavy appearance, while others have it as coarse as wire and as bright as a brick. ATMOSPHERIC TELEGRAPH.—We have received a letter from a Baltimore correspondent, who speaks disparagingly of the atmospheric telegraph of Mr. Richardson, which was illustrated two weeks ago in our columns. He wonders how men oi science can advocate it, as " the packages in the tube cannot be sent away faster than the air pump works, which exhausts the tube." This is true, but the difference is, that the air pump may be kept working constantly, while packages need not be sent but two or three times per day. He speaks of a locomotive being as last, and a much better way to send packages. Well, we have no doubt but a small locomotive and an airline oflilliputian railway would answer to carry packages if the plan could be carried out. A locomotive must stand idle when it is not working, but the atmospheric telegraph engine may be kept working day and night accumulating a force for the rapid transportation of a package, when it is to be s"nt. We hope the plan of Mr. R. will be successful, although we know there are many practical difficulties in the way, nothing but mechanical ones, however.