There are fortunately some American women left whose constitutions have resisted the effects of wrong living and bad such an extent that they can sit bolt upright for ?a considerable time without an excruciating pain in the small of the back, or walk a mile or two without being sick a day or two to pay for it. Women of thiskind can operate a sewing ma-! chine at intervals without discomfort, or may follow it as a business without evil consequences. But precisely those who from enfeebled health most need the aid of this invaluable invention, are the ones who are debarred from its use. The effects produced on the latter class of females by the use of the sewing machine have been thoroughly studied, particularly in Prance, and have been found to comprise a variety of ills peculiar to the sex most employed in such labor, which it is unnecessary to enumerate here. It is estimated that over a million sewing machines are now at work in the United States alone, and it has become a fact recognized both in this country and abroad that the prevalence of pallor, lassitude, pain in the back, and leucorrhcea are more prevalent among those who work with sewing machines than among almost any other class of women. Since our publication of an article, entitled " The Sewing Machine, its Origin, and Suggestions for its improvement," to be found on page 246, current volume, we notice the subject has been taken up and discussed at length by the press of this city, and a large number oi improvements have been suggested to obviate the use of the feet in driving sewing machines ; but it should be remembered that it is not the amount but the kind of work performed, that results in injury. A small cheap motor would be very useful, but an application of the power of the body in a manner free from the objections of the treadle motion would be better. The slight swaying of the body from side to side, or a rocking motion might be utilized for this purpose, or the weight of the body raised at intervals might be called in, as a sufficient force for the purpose. There is a demand for some improvement in the mode of applying power. Ii motor machines are relied upon for the purpose, they must be of the simplest character, durable and capable of being operated by any one ; and both constant and uniform in their action. The latter consideration will for the present exclude electro-motors from competition without taking into account the cost of running such machines by any form of battery now known. Small portable steam engines, are the next most promising resource, but they cost money to make, and money to run them, take time to get up steam, and are otherwise ill adapted to the purpose. Spring motors are liable to get out of order, and the winding them up is one of many objections against either them or weights. It has been proposed that in large cities small hydraulic engines might be successfully introduced for this purpose, but the impracticability of this will be apparent from the following computation : The power of the average human frame, is 4,166'6 footpounds per minute. Estimating the power required to drive a sewing machine as one-tenth of this, we shall have in round numbers, 466 foot-pounds, amounting per day of ten hours to 279,600 foot-pounds. Allowing the average head in upper and lower stories of buildings to be 30 feet, it will require for a single sewing machine tie fall through that head of 9,320 pounds, or in round numbers 148 cubic feet of water per day. If all sewing machines in New York city were to make this extra demand upon the resources of the Croton Board, it would find itself seriously embarrassed to meet it with the present supply. A small gas engine seems to offer more points of feasibility than anything we can think of, provided the necessity of using an electric discharge to ignite the gas, could be obviated by a cheap and efficient substitute. The fact remains that a small and reliable motor is very much wanted for this purpose and inventors would do weTl to grapple at once and vigorously with the problem. " First come first served," is the rule in invention, and he who can bring out the first sewing machine motor,fully adapted to the requirements of the case, is a made man. Any such machine would also find a wide application for a host of domestic purposes, as well as in the requirements of light manufacturing.