Books on elementary engineering are not scarce, tut good ones are exceedingly rare. The above is the title of a new took publish ed by C. A Brown & Co. Phila., the editor is Oliver Byrne, Mathematician, Civil, Military, and Mechanical Engineer, the author and compiler of a long list of books, Surveyor Ge neral of the Falkland Isles, Professor of Ma thematics in the College for Civil Engineers London, etc., etc., etc. Such a distinguished and talented man of science should be able to produce a good book surely, but it appears to us that the long string of titles on the title page, is intended to astonish the ignorant na tives of these United States with a profound reverence for the supreme erudition of the professor. Our practical workingmen, foi whom the book is specialy designed, are too well read and instructed in both the theory and practice of their professions not to know wheat from chaff. The author says, " no apology is offered for the mathematical proofs that set aside errone ous doctrines or establish new facts, however illustrious the propounder." By-and-by we will present one of these new facts. On page 107 he lays down the principles upon which practical mechanics are based and machines operate, which he calls " an exposition of the false mechanical doctrines promulgated by Newton, Hutton, Gregory, Robinson, and other English writers, which erroneous doc trines are yet taught in schools, colleges, and by public lecturers." In the whole of his ex position we perceive nothing new or original. The chapter opens with an account of the dispute between Newton and his friends on one side, and Liebnitz and his friends on the other side, about the measure of mechanical force. Newton, he says, was on the wrong side, and in another place he tells us the dis pute was dropped " because it was observed that the different properties expressed by wXv Newton's formula) and uXv*Leib nitz's formula) were not at variance." How, then, could Newton be on the wrong side.— Again, we are told " the terms momentum and impetus removed the ground work of the dis pute." The dispute then, if these two terms removed its ground work, was anything but a creditable one for such famous mathemati cians. The exposition, however, of the errors of Xewton, Huttpn, &c, would have been more creditable to the modesty of the expo-ser, if he had told us whence they were deri ved, such as pages 53 and 54, &c, Vol. 2, second series ot the Glasgow practical Me chanics' Journal and Engineers' Magazine, the editor of which being one of those writers whose erroneous doctrines on mechanics Mr. Byrne exposes by using his own works (Mr. Johnstone's) for that purpose. James Watt comes in for a slapdash attack too. Respecting the nominal horse power oi an engine he says: ''Such silly calculations are of little value although laid down by that great Scottish celt James Watt who was taught by an Irish celt, Dr. Black; the nomi nal horse-power of a high pressure engine has never been defined." The remark about the nominal horse-power of an engine never hav ing been defined, is certainly very funny, and exhibits an extensive acquaintance with the English language. The slur about Watt is a libel on all the celts, it is as much as to say, " he could not but be a silly calculator, when taught by an Irish celt. The eminent Dr. Black was not an Irishman but a French man ; the author must have made a mistake in substituting a different native place from the real one of Dr. Black, as he substituted the matter of the " Practical Mechanics' Ma gazine " for his own. Let us now speak of a new fact discovered by the author, it relates to the causes of steam boiler explosions. He says, "Mr. Oli ver Byrne has discovered that the true cause of the explosion of boilers is the introduction of the medium of space." Let us quote his own words respecting the whole of this won derful discovery. He says:— " When the boiler is supplied with an in sufficient quantity of water to compensate for that which is converted into steam the water within is lowered, and the steam takes a temperature that has not a corresponding elastic force as the moisture to supply propel density is denied. Of this the ordinary safe ty-valve gives no indication, and if it be opened it produces an explosion; the steam rushes out in a conical form, base uppermost: this leaves a space in the centre of the cone; through which the medium of space enters. An explosion may be produced without rais ing the safety valve, for a supply of watei suddenly introduced will produce the same effect" Now we think the above is something which will open the eyes and ears of our practical engineers. Here we have one oi the grandest discoveries of the age presented to us, viz., the cause of steam boiler explo sions. This medium of space we think must be a " banshee." The hint about such a cause we have read of before, in the description given by an English engineer of the introduc tion of the first steam engine to Hindoostan. The natives believed that an English spirit was in the boiler, and he would not work un til well roasted, when off he went with a scream. The engineer taught the Hindoo fireman that if he did not provide a sufficient supply of water to the spirit in the boiler, he would break out and destroy the whole country—this spirit was no doubt the Hin doo medium of space, for as spirits can enter the key hole of a door, one can surely find no difficulty in entering a steam boiler through the small space in the centre of a cone of sur charged steam. The above quoted paragraph is certainly the richest, funniest, and most wonderful one we have come across in any work on engineering in the 19th century.— We have always understood that all matter was a medium of space, but it seems that there is something else which is a medium of space, consequently matter will have to be set down after this as a spiritual medium which will at once open up another field of discove ry, and reveals to us the cause of the spiritual rappings, tables moving, &c.