Differential Screw Research Articles

The Design and Construction of a Differential Refractometer for Measurements on Coloured Solutions

A differential refractometer, suitable for the measurement of refractive indices of dyes, is described and some of its uses are indicated. The instrument is of the prism type, utilising a small spectrometer to provide monochromatic light. Refractive index values are obtained by means of a rotating mirror driven by a differential screw, which cancels the deviation conferred on the light beam by the dye solution.Several advantages of the instrument for measurements in spectral regions of maximum absorpation are discussed.

Use of acrylic prosthesis in the treatment of fracture of the head of the radius.

Use of acrylic prosthesis in the treatment of fracture of the head of the radius.

Barton‘s Ruling Engine

IN the possession of the Science Museum, London, there are six beautifully engraved buttons, classified as diffraction gratings, which are still regarded as masterpieces. They were the work of Sir John Barton, deputy comptroller of the Royal Mint in the early part of the nineteenth century, about whom little is known personally, but who must have been an ingenious inventor and capable engineer, for in 1806 he invented a differential screw measuring instrument capable of measuring to 10-5 inch. In 1822 he was granted a patent for his engraved buttons. After Sir John‘s death the ruling engine on which the buttons had been ruled passed into the possession of his grandson and then to his great-grandson, Mr. R. V. Barton, who, in 1925, presented the engine, together with some handwritten notes of his father‘s concerning the working of the machine, to the Science Museum. The above details are given in a valuable and interesting illustrated article entitled "A Ruling Engine Used by Sir John Barton— and its Products"which P. Grodzinski, the technical editor of the Industrial Diamond Review, contributes to the February number of that journal. It would appear that this is the first authoritative description.

A Microtome Sectioning Technique for Electron Microscopy Illustrated with Sections of Striated Muscle

The preparation of histological and cytological sections for study with the electron microscope presents several difficulties. These are due chiefly to the necessity of drying and to the low penetrating power of electrons. The distortion commonly attendant on air-drying can be obviated by vacuum-drying in the frozen state. The low penetrating power of electrons is more serious since for high resolution electron micrographs it has been found that sections must be less than 0.25 ν and preferably less than 0.1 ν thick. von Ardenne has described a method, but, judging from the one micrograph published, his sections were not sufficiently thin for good resolution or adequate penetration. The present paper describes a technique by means of which relatively uniform 0.1 ft sections of striated muscle have been prepared and examined with 60 kV electrons. Some types of material can be cut freehand but much histological material requires a microtome. No commercial microtomes cutting such thin sections are now available but standard commercial models can be adjusted by a number of different ways to cut thinner sections. Our machinists have suggested three methods for adjusting microtomes to cut at fractions of a micron: (1) For Minot and similar sliding microtomes the cam knob that hits the setting device to control the movement of the ratchet wheel may be machined so that it has 4 quadrants each with a different radius. The radii can be adjusted so that with the machine set to cut at one micron the micrometer screw moves only approximately one-quarter of a micron (one-quarter of a tooth-spacing on the ratchet wheel) at a stroke, the cam knob being turned by hand between strokes. (2) The single micrometer screw used to move the specimen may be removed and replaced by a differential screw.

Month in the Patent Office

A variable‐pitch airscrew includes a differential screw mechanism connected with two skew gear‐wheels of opposite sense, mounted coaxially of the airscrew shaft, said skew wheels being adapted to be restrained against rotation for the purpose of altering the pitch of the propeller blades. Within the hollow driving shaft of a propeller are two coaxial shafts 17, 18 having at their inner ends spur wheels 23, 24 which are in mesh with corresponding teeth formed on two brake drums 23a, 24a that are furnished with brake bands 23b, 24b controlled by a lever 26c. The outer ends of the shafts 17, 18 carry skew gear wheels 29, 30 of opposite sense which engage permanently pairs of gear wheels 31, 32, and 33, 34 mounted on parallel transverse shafts 35, 36 and 37, 38. The shafts 35, 37 are connected by means of right and left‐hand skew gears 39, 40 with a transverse rotatable sleeve 41 splined on to a shaft 44. This shaft 44 bears two differential screw threads 45, 46, the smaller of which 46 engages a threaded boss 47, whilst the other engages a screwed lug 48 on a slidable sleeve 55 having an open jaw member 57 which engages an eccentric pin 58 at the root of a blade. When the hand lever 26c is moved to brake one or other of the wheels 23, 24 one or other of the skew gears is given a relative rotation and a corresponding movement takes place of the shaft 44 whereby the blade is altered in pitch. As an alternative to the brake drums the shafts 17, 18 may be furnished with notched discs adapted to be engaged by spring‐influenced pawls carried by a lever similar to the lever 26c.