Scientific American Supplement No. 822, October 3, 1891 eBook

This eBook from the Gutenberg Project consists of approximately 149 pages of information about Scientific American Supplement No. 822, October 3, 1891.

This would be unnecessary for the end in view, and impossible on account of the amount of time that would be required.


It is of the greatest importance that the polariscopes and all apparatus used in the work shall be carefully and accurately adjusted and graduated, and upon a single and uniform system of standardization.  Recent investigations of the polarimetric work done in the customs branch of the Treasury Department have shown that a very considerable part of the want of agreement in the results obtained at the different ports was due to a lack of uniformity in the standardization of the instruments and apparatus.

(a.) The Polariscope.—­There are many different forms of this instrument used.  Some are adapted for use with ordinary white light, and some with monochromatic light, such as sodium ray.  They are graduated and adjusted upon various standards, all more or less arbitrary.  Some, for example, have their scales based upon the displacement of the polarized ray produced by a quartz plate of a certain thickness; others upon the displacement produced by an arbitrary quantity of pure sucrose, dissolved and made up to a certain volume and polarized in a certain definite length of column.  It would be very desirable to have an absolute standard set for polariscopic measurements, to which all instruments could be referred, and in the terms of which all such work could be stated.  This commission has information that an investigation is now in progress under the direction of the German imperial government, having for its end and purpose the determination of such data as will serve for the establishment of an absolute standard.  When this is accomplished it can easily be made a matter of international agreement, and all future forms of instruments be based upon it.  This commission would suggest that the attention of the proper authorities should be called to the desirability of official action by this government with a view to co-operation with other countries for the adoption of international standards for polarimetric work.  Until this is done, however, it will be necessary for the Internal Revenue Bureau to adopt, provisionally, one of the best existing forms of polariscope, and by carefully defining the scale of this instrument, establish a basis for its polarimetric work which will be a close approximation to an absolute standard, and upon which it can rely in case of any dispute arising as to the results obtained by the officers of the bureau.

For the instrument to be provisionally adopted by the Internal Revenue Bureau, this commission would recommend the “half shadow” instrument made by Franz Schmidt & Haensch, Berlin.  This instrument is adapted for use with white light illumination, from coal oil or gas lamps.  It is convenient and easy to read, requiring no delicate discrimination of colors by the observer, and can be used even by a person who is color blind.

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Scientific American Supplement No. 822, October 3, 1891 from Project Gutenberg. Public domain.
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