In our article on the " Effect of Sewing Machines upon Female Health," published on page 378, current volume, we made a statement in regard to the power required to drive a sewing machine, estimating it as being one tenth the power of the average human frame. The total power of the human body was estimated at 4,166"66 foot-pounds per minute, which would give for the power required to drive average sewing machines, according to our estimate, in round numbers, 416 foot-pounds per minute. In some inexplicable manner a blunder wa.s made in the first division by ten, the quotient of which was put down as 466instead of 416foot-pounds. The final result was, of course, vitiated by this error. It should have been 249,600 foot-pounds per day of ten hours, instead of 279,600 footpounds, as stated, equal to 132 cubic feet of water falling 30 feet instead of 148 cubic feet. Our estimate has been criticized as being evidently too large. It was based upon some rude experiments with an improvised apparatus, with which, however, we obtained results which assured us the amount of power we- stated was sufficiently within bounds. As our estimate was questioned, we took the trouble to call upon several manufacturers, every one of whom assured us that our statement must be nearly correct. It was, however, only at one establishment we could find any positive information. By the courtesy of Mr. J. M'Call, the gentlemanly manager of the Elliptical Sewing Machine Company, we were able to gain the following important facts, which will be of use to all interested in sewing machine motors. First, it takes on an average, one eighth of a horse power, furnished by steam or other motive power, to run one sewing machine; three fourths of the power being lost or wasted in stoppages, in checking the motion of the machine, in running slow and fast, etc., etc. It is from not appreciating the great loss oi power arising from the above causes that most of the motors invented for this purpose have proved failures. When the ordinary treadle motion is used, if proper adjustments are made, one thirty-second of a horse-power will do the work or a little more than one thousand foot-pounds per minute. This makes the average power required about one fourth of the power of the human frame. But as many machines run much lighter than the average, we are assured that our estimate intended for the power required for domestic machines and light sewing, is not far out of the way, and that it is certainly within bounds. The figures obtained from Mr. M'Call are based upon actual experiment. It is a common error to estimate the power required to drive small machines entirely too low. We venture to say that were the generality of mechanics to estimate without test the number of watches that could be driven by one horse-power, they would be more' likely to make the number double what would be correct, than to make it less. The cause for this arises from the want of a proper appreciation of the difference between the total power of a motor, whether animal, man, or steara engine, that can be exerted for a short time in case of an emergency, and that which it can do continuously. A man can run for a short space almost as fast as an average horse. Without doubt many men can run at the rate of a mile in four minutes for a short space; but few men can accomplish four miles an hour for ten hours. An average man could probably raise, under favorable circumstances, twelve thousand pounds one foot high per minute for one or two, or perhaps five minutes, but put him at continuous lifting and he cannot do half that. It takes but little power to move the treadles of a sewing machine once; but to do it one hundred times a minute, or even sixty times, is another matter; allowing a small quantity of force only to each half stroke, a computation will show the aggregate for ten hours to be something considerable.