This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1882 Excerpt: ...of observations should be taken. As a rule, five observations in each quadrant will be enough, so that allowing for the verification of the zero-points, which should be repeated at least once each day on taking observations, the angle of rotation finally obtained will be the result of forty readings. Where considerable differences are found in the readings, the number of observations must be increased.2 This will occur when the solutions are not absolutely clear; slight colorations, on the other hand, do not materially affect the observations. The degree of accuracy attainable is shown in the two series of observations appended. These were taken with an instrument of Hermann and Pfister's manufacture, graduated to divisions of 5 minutes, and allowing of approximate reading to single minutes. The liquid employed was an aqueous solution of cane-sugar containing 19-4-5 grammes in 100 cubic centimetres. The length of tube was 21979 millimetres. 1 van de Sande Bakhuyzen: Pogg. Ann. 145, 259. 2 Differences of 20 minutes in the readings may easily occur with unpractised observers, but with care these can soon be much reduced in amount, so that a hasty opinion should not be formed of a newly-purchased Wild polariscope. When the observer has become accustomed to the instrument, and the latter is properly constructed, the difference in the readings will seldom exceed 5 minutes. 0 20-0-28 43-8-90 19-0-, 118 40-0 o = 28 23-8-or= 28-397 28 21-0-28-350 180 13-8-208 38-6 v j, / 28 24-8-28-413. 28 29-0-23-483 Mean of Quadrants I. and III. 28 24-3-= 28-405. II. „ IV. 28 25-0-= 28-417. I., II., III., IV. 28 24-65-= 28-411. Mean of Quadrants I. and III. 28" 24-1-= 28-402.,,., II. „ IV. 28 24-7-= 28-412.,, I., II., III., TV. 28 24-4-=28-407. (c.) Half-Shade In...
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