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away with all calculation on the part of the observer. It mechanically records the difference in the power in dioptres and the exact nature of the astigmatism. The dial plate also records the curvature in dioptres together with the radius of the cornea.

There is one continuous mire, the equivalent of the ordinary two mires ; the whole of the mire is utilised, and there are no confusing extra images, and as the mire is stamped out of one piece of metal, it is impossible for it to develop the common fault of mal-alignment. The original single image of the mire is trebled by the cylindrical prisms. Thus all the images are decentred diagonally in opposite directions, the first up and to the right, the second down and to the right, the third down and to the left. The slides cause the horizontal outside image to approach the corner stationary image, and in similar manner the vertical image moves downward. Although the decentration is oblique, the approximation is vertical and horizontal.

Stevens Phorometer.

The Steven’s phorometer is fitted with two cells, each containing a 5° prism. The two are connected together by a small gear wheel, fitted between the two prism cells ; the frame containing these is pivoted on a fitting connected to the arm. A small milled head with back spring is provided for levelling the instrument, a level being fitted in the frame. Scales marked in gold on black are fitted around the. cells, and read from centre each way from 0° to 10° the numbers representing the refracting angle of the prisms.

Phoro-Optometer.

This instrument is a combination of the revolving three cell gear driven trial frame; the multiple and single red Maddox rod for each eye ; the Steven’s phorometer, with spirit level, and a graduated adjustable near point test; all so arranged as to be used separately or collectively as desired.

The adjustments for pupillary dimensions, cylinder axis, and prism powers, are all accurately and plainly graduated in gold on black and are larger than in the earlier models. They are fitted in friction tight bearings giving an ease and smoothness of movement seldom found.

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,91 %.

La langue de reconnaissance de l'OCR est l'Anglais.