158 



VII. — Amstutz Optical Micrometer. 

 By Marshall D. Ewell. 



{Bead January 19, 1916.) 

 Fig. 7. 



In the practice of microscopy, the ability to measure thicknesses 

 of sections, etc., by means of a graduated fine-adjustment in parts 

 of a micron has meant much in setting; the bounds for a most 

 exact science; likewise the use of an ocular micrometer, filar or 

 otherwise, has been of inestimaljle assistance in establishing 

 definiteness of lineal dimensions. So far, however, it seems that 

 little, if anything, has been done to make use of a deiiuite dimen- 

 sional scale combined with the folding elements of a single-lens 

 pocket magnilier suitable for field work, and a multitude of other 

 pur])Oses, when magnifications of the order of about 13 diameters 

 are used. 



Such a magnifier has been devised by Mr. N. S. Amstutz, 



Fig. 7. 



Eesearch Engineer, of Valparaiso, Indiana. It is built much more 

 stocky than the well-known French type of linen-tester. They 

 are made in two forms — a ^-in. opening and a j-in. opening, 

 selling respectively at £1 and 12s. 6d., post paid, including a 

 leather case. The lenses are ordinarv double-convex of about 

 0'8 in. focus. At the low magnification used it is scarcely found 

 necessary to have an achromatic or aplanatic lens. The scales lie 

 directly on the object being examined, hence the spherical aberra- 

 tion of an uncorrected lens is the same for the scale and the object, 

 making the error of no practical moment. As the scales are in 

 contact with the object there is no serious parallax error. The 

 scales are ruled on brass strips which are secured on a bevelled 

 seat sloping toward the actual centre of the lens. Different rulings 



