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Show PERSONAL EQUATIONS. A Machine That Corrects I'rrors Thai Humanity Can't Help but Make. Carleton college observatory ban just secured a curious instrument invented by a scientist at Washington and called a "personal equation machine." The object of the instrument is to ! harmonize the observations of different persons who are working together, at different times or at the wane time. Astronomers As-tronomers well know that no two persons per-sons see exactly alike, by which is meant, for example, no two persons will say that a star passes a wire iu a telescope it exactly the same instant. One will record its apparent passage slow on true time, while another will almost uniformly uni-formly put its time fast. Observers unconsciously form a habit of seeing objects, fast or slow, on true time, and tho better the observers are the more steady this error is as compared with true time. This error the astronomer astron-omer calls the personal equation of the observer. In amount tho personal equation equa-tion varies from 0.03 of a second of time to something more than half a second for different oliscrvers, cither fast or slow on true time. .Such errors as those cannot be tolerated at all in astronomical astronom-ical observations for fundamental or original work of a nice kind, hut must b-,-in some way eliminated before final reductions can lie attempted. To accomplish this, in one way, an ingenious in-genious mai'hiiio has been constructed which sets in motion an artificial star, quite like the appearance of a real slur., in the t' leseope. As this artificial star passes win s in the machine the observer records his observations, and the instru t ment automatically records tho exact ' time of the real passage of tho star over i tiie name wires. A'ow both records are ; made by the aid of tho electric current, and consequently are perfectly true. These records are taken automatically in ink on an instrument called a chro iioiiii ter, and hence their differences can i bo measured wilh tiio utmost accuracy, j and in this way the crryrs of the obser- I ver on true time are known. The machine is in use every night that . observers work cither together or singly, j so that changes in individual jiersonal equations maybe detected, as well as the differi'iiecs that may exist between observers. ob-servers. The instrument, therefore, furnishes fur-nishes an unvarying standard for accurate accu-rate observations. Cor. St. Paul Tio-Uccr Tio-Uccr Tress. |