ATMOSPHERIC TELEGRAPH.—We have received a communication from a correspondent who points out some difficulties in the way o: the successful operation of an atmospheric telegraph. The first objection is, " 1st. a perfect vacuum cannot be formed in the tube ; 2nd. The tubes must be accurately bored out and fitted perfectly straight ; 3rd. The piston must be packed, causing great friction, impossibility of oiling, and hence the packing musl heat." We have said before, that the difficulties ir the way of its successful operation, are mechanical. If these can be overcome, there ii no reason why it should not operate. We an well aware of the impossibility of forming t perfect vacuum with the best air pumps ; anc so are those connected with the Boston Atmospheric Telegraph. It is not positively necessary that the tube should be perfectly bored throughout; the packing of the piston obviates the necessity of having a perfect tube, We could not raise an objection against Vat plan by saying "the piston will heat," andwt are positive that ourconespondent has no correct information on this point. There are difficulties in the way of fi successful atmospheric telegraph ; if there were none, the system would have been in operation long ago. The question is, does Mr. Richardson's plan remove them ? This question, on a small scale has been settled, and it will soon be, we have been informed, on a large scale. A BRIGHT IDEA ABOUT HEAT."Suppose all the obstacles to the perfect and economical transfer of heat removed, so that all the heat in a cylinder full of steam could be transferred from the exhaust to the contents of the steam pipetransferred from the outgoing to the in-coming medium, what would be the total mechanical effect of a unit ol heat." The above we have quoted from a scientific cotemporary, who calls for some one to answer his query. We refer him lor an answer to the gentleman who made the discovery that 1 lb. of coal can be made to pump the Niagara river dry in a day. Instead of progress having been made in physical science, we sometimes think, from the stuff uttered by pretenders to scientific knowledge, that there never was such a dearth of the genuine article. The above quoted paragraph simply means, " what would be the mechanical effect of a unit of heat in a steam engine, by exhausting into the boiler." The absurdity of the question shows the depth of the interrogator. A SIMPLE FIRE ANNIHILATOR.We perceive that a cotemporary speaks of sulphur as being an effective and simple fire annihilator, and tells of an insurance agent of Troy, N. Y., who recommends it as having been efficacious in one case, of saving his property. It is not a little remarkable that many discoveries are continually being developed some years after they have been described in our columns, and this is one among a number of others. If any person will turn over to page 2, Vol. 7, Scientific American, he will see in some comments upon the once celebrated 'hillips' Fire Annihilator, that we distinctly mentioned sulphur as having been successful-y used for extinguishing fires in chimneys. Improved Mode of Casting Pumps. An improvement in pumps, by John H. Me-Gowen, of Cincinnati, Ohio, to which this invention forms a necessary appendage, has al-eady been noticed in the Scientific American. Vfr. McGowen has a mode of casting his pump, which renders it a much better article han those cast by the old process, and also enders the operation of casting much easier, n this operation the cores which form the in-erior chamber of the pump, are moulded up-n the top ot what is called the " knowl " or drag," in such a manner that they will ad-ere thereto, and thus keep all the cores in aeir proper vertical position while the metal s poured. By this arrangement pumps o lis description may be cast on either green r dry sa-,d with equal facility. The inven-or, Mr. McG., has taken measures to secure a latent.