Page:Popular Science Monthly Volume 15.djvu/717

 burned so as to transfer from seventy to seventy-five per cent, of its theoretical heat to the boiler, and I do not know that this is the best attainable. Mr. Wahl's limit of twenty-five per cent, efficiency of fire-box, or, as he well terms the boiler and fire-box, the "steam-generator," is therefore entirely too low; neither has he mentioned the principal cause of the loss of heat in steam-engines, viz., the low efficiency of steam as a medium on account of its high latent heat, a very small part of which, at best, can be utilized even in condensing engines, and still less in non-condensing engines. In locomotive-engines the following statement will represent a fair average performance, with corresponding approximate rates of loss from different causes:

The low efficiency of the steam stands somewhat as follows:

which can not be converted into work in the locomotive-engine: neither is the difference 1,160 $$-$$ 865 $$=$$ 295 all available; for 212 $$-$$ 60 $$=$$ 152 of this was required to heat the pound of water to the boiling-point at atmospheric pressure, and still more at one hundred and twenty-five pounds' pressure. This reduces to 295—152=143 units, all of which is not obtained from each 1,160 units expended, for the steam is exhausted at some pressure above atmosphere to get more work from the engine and to blow the fire, so that we really get but about ninety useful units out of 1,160 expended, or about eight per cent. In best stationary engines (which are to yield fifteen per cent, efficiency) this would stand:

The twenty per cent, here in place of the eight per cent, in locomotives is because of expanding steam to a lower pressure before exhausting, of the partial vacuum ahead of piston from condensing exhaust steam, and of the heated feed-water which should be credited to this account of efficiency of steam. I can not here go into the experiments of M. Hirn, and conclusions therefrom, on the beneficial influence of partial condensation on steam side of piston, but the above figures, so far as they go, will nearly represent the facts of efficiency. I think you will do your readers a service by correcting, even in this general way, the wrong impressions they may have received from Mr. Wahl's figures.

Messrs. Editors.

by your correspondence that there is some interest taken in spiritualism.

A case occurred in my experience some fifteen years ago which, for a while, made a profound impression on my mind. My house is situated about three hundred feet from a large church, which has a fine organ, that we heard more or less, when played upon.

It was in the beginning of summer; the windows being open, myself and family heard more plainly than common, as we thought at first, the organ. It went through a chord producing at times what is called the tremolo. We soon ascertained, however, that these sounds did not come from the organ, but from the piano which stood in our double parlors. It went through a chord of quite a number of the lower notes, giving somewhat the sound of the organ. Being myself rather skeptical in matters pertaining to superhuman phenomena, I was touched profoundly by these manifestations.

Some of the more timid neighbors declared they would not live in the house; myself and family did not share these views. I stated to my friends that I expected to find some rational cause for this most extraordinary phenomenon. People wanted to come in droves to witness this new wonder, which I did not allow. Some spiritualists came from Boston, ten miles, to hear for themselves, and declared it must be produced by spirits from the other world. To this I could not assent, never having believed in spiritualism.

The Rev. Eli Fay, Unitarian, and now settled at Sheffield, England, and the Rev. Dr. J. C. Bodwell, Orthodox, now dead, both able, discreet men, spent with me considerable time in investigating the cause of these wonderful sounds. They examined the house throughout, including the cellar, without success. On one occasion one of my neighbors, being present, made the inquiry, "Who have played most on your piano, who are now dead?" My answer was, his own wife, now dead, and the daughter of one of my near neighbors. He then replied, "Is it possible that Caroline's spirit" (meaning his wife) "is there?"—when the piano seemed to go through a chord louder than ever before, and almost made the hair stand erect on our heads.

And so it continued for some days, until one evening I sat on the front stairs reading the evening paper, there being no gas burning in the house except in the hall, and my family were out. My attention was attracted to a very different sound, not musical, coming apparently from the piano. I stepped into the parlors—still the noise continued. I now lighted the gas in the parlors, when