It often becomes necessary for the experimenter or practical worker to find the thickness of material so thin, or inconvenient to measure, that the thickness cannot be found by means of a foot-rule, or other common measuring device. A simple, fairly accurate, and easily-made apparatus of the micrometer form may be constructed as follows: Get a common iron or brass bolt about y of an inch in diameter and about 2% inches long, with as fine a thread as possible, and the thread cut to within a short distance of the head of the bolt. A bolt with a cut in the head for a screw-driver should be used. Clamp together two blocks of wood with square corners about 1 inch wide, % of an inch thick, and 2% inches long, with their narrower faces in contact (the width of the clamped blocks being two inches), and bore a -inch hole through the center of the blocks in the 2-inch direction. Now remove the clamp, and let the nut of the bolt into one of the blocks so that its hole will be continuous with the hole in the wood, then glue the blocks together with the nut between them. Cut out a piece from the block combination, leaving it shaped somewhat like a bench, and glue the bottoms of the legs to a piece of thin board about 2y2 inches square for a support. Solder one end of a stiff wire about 2 inches long to the head of the bolt at right angles to the shaft, and fix a disk of heavy pasteboard with a radius equal to the length of the wire, and with its circumference graduated into equal spaces, to serve in measuring revolutions and parts of revolutions of the end of the wire, to the top of the bench; put the bolt in the hole, screwing it through the nut, and the construction is complete. The base is improved for the measuring work by gluing to a central section of it, covering the place where the end of the bolt meets it, a small piece of stiff metal; and it is convenient to have the graduated disk capable of rotating, so that its zero line may be made to coincide with the wire. Find the number of threads of the screw to the inch by placing the bolt on a measuring rule, and counting the threads in an inch or half an inch of its length. The bolt in making one revolution will descend a distance equal to the distance between the threads. To use the apparatus, put the object whose thickness is to be measured on the base under the bolt, and screw the bolt down until its end just touches the object, then remove the object, and screw the bolt down until its end just touches the base, carefully noting while doing so the distance that the end of the wire moves over the scale. The part of a rotation of the bolt, or the number of rotations with any additional parts of a rotation added, divided by the number of threads to the inch, will be the thickness of the object. Quite accurate measurements may be made with this instrument, and in the absence of the expensive micrometer, it serves a very useful purpose. I have used it in the beginning classes in electricity for measuring the diameter of wire, for finding the numbers of wires from reference tables, and for making various other measurements. The Current Supplement. Prof. George Lunge opens the current SUPPLEMENT, No. 1667, with a thoughtful article on the problems of applied chemistry. An apparatus for electrical vision is described under the title of the "Senlecq Telectro-scope." A most helpful and practical article is one entitled "Some Soldering Appliances." Particularly timely at this season of the year is an article on preventing frost on show windows, in which article various methods of keeping glass clear in cold weather are described. William Mayner writes on some Prussian railroad tests made near Oranienburg, the object being to determine the best track. Frederick C. Cole-man contributes a very interesting and excellently-illustrated article on a new cable ship, and describes the machines which are used for laying submarine cables. The action of sea water on concrete is discussed. The defects of the first British airship are enumerated in an article in which the need of harbors for aerial craft is dilated upon. For many years past pottery models of houses occasionally found their way into museums from the illicit digging of natives in Egypt, but nothing was known as to their original positions and dates, and they were so scarce that not even the National Museum at Cairo had any sample. Prof. Flinders-Petrie explains the meaning of these houses which, it would seem, had a peculiar religious significance. Few persons appear to be acquainted with the proper meaning of the word "coney" used in the Bible. Mr. R. Lydekker tells just what the coney is. Arthur Stentzel writes on the climate of Mars, and notes its effects upon the habitability of the planet. Official Meteorological Summary, New York, N. Y., November, 1907. Atmospheric pressure: Highest, 30.55; lowest, 29.16; mean, 30.04. Temperature: Highest, 60; date, 2d; lowest, 33; date, 30th; mean of warmest day, 54.5; date, 6th; coolest day, 36.5; date, 14th; mean of maximum for the month, 50.1; mean of minimum, 40.4; absolute mean, 45.2; normal, 43.8; excess compared with the mean of 37 years, +1-4. Warmest mean temperature of November, 50, in 1902. Coldest mean, 37, in 1873. Absolute maximum and minimum of this month for 37 years, 74 and 7. Average daily deficiency since January 1, 1.0. Precipitation: 5.05; greatest in 24 hours, 1.90; date, 6th and 7th; average of this month for 37 years, 3.50. Excess, +1.55. Accumulated excess since January 1, +0.19. Greatest November precipitation, 9.82, in 1889; least, 0.82, in 1890. Wind: Prevailing direction, west; total movement, 8,699 miles; average hourly velocity, 12.1 miles; maximum velocity, 52 miles per hour. Weather: Clear days, 8; partly cloudy, 9; cloudy, 13; on which 0.01 inch or more of precipitation occurred, 11. Snowfall: Trace. Mean temperature of the past autumn, 55.17; normal, 55.20. Deficiency, 0.03. Precipitation for the same season, 16.87; normal, 10.89. Excess, +5.98. A New Anaesthetic. Mr. F. W. Malvin, United States consul at Nottingham, sends to the Bureau of Manufactures at Washington some particulars concerning the new anaesthetic, stovaine. It appears that it produces paralysis of the body below the point of injection and removes all sensation from the limbs, so that it has been found possible to amputate a man's leg while the patient retained consciousness, and could, had he been allowed to do so, have even witnessed the operation. The patient could feel no pain, and after the operation and when sensation returned experienced nothing but the sense of bruising, which is one of the sequels of grave operations. The curious name of the anaesthetic, "stovaine," is due to its discoverer, M. Fourneau. M. Fourneau was anxious to perpetuate his own name in connection with it, but as the anaesthetic was of the nature of cocaine and no compound resembling that could be contrived out of "Fourneau," he translated the name into its English equivalent of "stove" and added the necessary termination. As the accuracy with which drill bits are formed and sharpened has a great influence on the capacity of a rock drill, and also as the maintenance of drill steel is one of the most important items in the cost of rock drilling, experience has shown that all mines using a considerable number of drills should include one or more drill-sharpening machines in their equipment. Drills sharpened by machinery are more perfect than those sharpened by hand, and the saving in cost will in a short time pay for the machine. The saving in labor alone is estimated as amounting to tt least 65 per cent.
An Easily Made Micrometer
This article was originally published with the title "An Easily Made Micrometer" in Scientific American 97, 24, 443 (December 1907)