carriage of the lathe. The microscope f, also attached to the carriage, is adjusted over a scale g, which rests upon a plate h. This plate is attached to the lathe bed. It has a fulcrum at h1, and an adjustable movement in elevation by means of a screw 2. Two or more flexure screws secure a parallelism of the upper surface of the plate at every point with the horizontal plane described by the carriage.

The shoulder next to the head stock is supposed to be already turned. The micrometer line of microscope f1 is then set upon the limiting edge and the zero of the graduations upon the bar g is brought into coincidence with the micrometer line of microscope f.

It is obvious that if the relative positions of the two microscopes remain unchanged, the distance measured on the scale by the

movement of the carriage will be indicated upon the shaft by microscope f1. It will be seen that by the use of two microscopes, the necessity of adjusting the cutting tool with respect to the fixed points of reference is entirely obviated. The position of the tool bears no relation whatever to the dimensions sought. When the first chip is taken-a little outside of the required limit the amount by which the carriage must be moved will be indicated by the micrometer line of microscope f1. It is to be noted, however, that the tool will do its work for one-quarter of a revolution before the amount of work done is indicated by the microscope, but the proper allowance can be quickly made by means of a graduated scale in the eye-piece of the micrometer of microscope f1.

In order to turn a face plate to a required diameter, adjust vertically the micrometer line of microscope i over the point of the face

plate which is stationary during its revolution. Adjust microscope upon the zero of the transverse scale. The required diameter will then be indicated by the movement of 2 over the scale and the indicated limit of the circumference through microscope i.

In order to turn a shaft to a given diameter, it is necessary to set the micrometer line of microscope in the line between the centers of the lathe. Since it is not possible to do this directly, we introduce an auxiliary measuring gauge kk, Fig. 68, which will also be found to be of great service in testing the various adjustments of the lathe. is a cylindrical shaft, ground to a true cylinder, e. g., in a Brown & Sharpe grinding machine, while supported at its centers. is a ring which slides freely upon the shaft and is capable of being firmly secured to k by projecting flanges (not

shown in the figures). This ring is also ground to a true cylinder and has a known diameter, e. g., of 3 inches.

When this shaft is placed between the centers of a lathe and 1 is set near the tail-stock, the projecting arm of a sliding arm m, Fig. 68, is brought into contact with the outside surface of 1, and the micrometer line of microscope m2 is set upon the zero of the scale upon the upper surface of the arm m. The shaft is now removed and the carriage is moved inwards through the space of 3 inches, as indicated by the scale. The micrometer line of the microscope will now be coincident with the line between the centers of the lathe, if the proper adjustment of the tail-stock has been made. It is not probable that this adjustment would need to be tested very often, if the microscope is firmly attached to the carriage.

If the point of the cutting tool is brought into adjustment under

the micrometer line of the microscope, the required diameter can be read off directly from the scale. Since, however, the wear of the cutting tool would probably be appreciable, this direct method of measurement would not probably be as satisfactory as the more indirect method of employing the additional microscope f1 in connection with an auxiliary calliper scale.

For any diameter up to about one inch with a 1-inch objective, we may proceed as follows. When the contact of the arm with the surface of the ring is made, set the micrometer line of microscope f1 tangent to the ring on the same side. Then, for any radius of the shaft to be turned, less than the working distance of the microscope, we shall have, after an inward movement of 3 inches, the micrometers of both microscopes coincident with the line between the centers of the lathe-one set upon the scale and the other over the shaft. The required diameter will then be obtained when the micrometer line of the microscope reaches the required point on the scale and the micrometer line of f1 is tangent to the circumference of the shaft.

With a slight vertical movement at right angles to the plane of the ways, microscope i might advantageously take the place of microscope f1. It would be necessary to raise the microscope in passing the center of the lathe, but since it would fall back upon the same scat, there would be little danger of disturbing the relative positions of the two microscopes by this movement.

In order to set the tail-stock for turning any required taper, set the ring at the end of the shaft adjacent to the head-stock and set the microscopes as described above. First set the ring at the point where the largest diameter is required, and then adjust the tail-stock in the usual way, so that the reading on the transverse scale shall indicate the lesser diameter.

It is obvious that two microscopes attached to the tool carriage of a planer, in connection with longitudinal and transverse scales, may be made to serve the same purpose as in the lathe. The microscope may be made especially useful in leveling up the bed of a planer. Place beside the lathe a shallow dish of mercury extending its entire length with means of adjustment similar to plate h, Fig. 67. Attach a microscope first to one end and then to the other end of the planer, and make the adjustment for level such that the surface of the mercury is sharply in focus under the microscope in the two positions. The bed-plate can then be blocked up at the intermediate points until every point is in focus.

With regard to the expense of fitting up a lathe with the microscopic attachments indicated above, it may be estimated at about $125, exclusive of the cost of the graduated scales. Only two objectives would be needed, at a cost of $20 each.

If it is urged that this direct process of applying dimensions in mechanical construction is not practical, or not well adapted to ordinary machine-shop practice, if it is insisted that the calliper must be used, I shall still maintain that a reform is needed in the method. of setting the calliper for a required measure of length, and that there is a better way than that ordinarily followed. It is simply impossible to set a calliper with any degree of precision from a

line scale. End-measure ganges are expensive and they require the most careful manipulation. Moreover, as ordinarily made, they can only be used for aliquot parts of a given unit. They are useless except for a few special lengths, and the extreme length seldom exceeds 6 inches.

There are four requirements which ought to be met absolutely in any proposed system of obtaining and transferring measures of length.

First. All measures of length must be referred to one linemeasure standard. This standard should be at least one yard in length, and the subdivisions should be such that any required length can be taken from it directly to 1 inch. Subdivisions less than

this limit can be better obtained with the aid of an eye-piece micrometer in the microscope. The yard should be standard at 62.0° Fahr., and the subdivisions should be so exact that there would be no necessity of applying corrections.

Second. The calliper gauge from which measures are to be taken for use in the machine-shop must be universal in its action. It must be capable of being set to correspond to any required length, aliquot or fractional, as indicated upon the line standard.

Third. It must be so simple in form, so direct and so sure in