The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . read by microscopes, and the instrumentcan be used in both positions (tube precedingand following) for elimination of the effect 0Iflexure on the position angles. Elkin found thatthe chief drawbacks to speed and conveniencein working this heliometer were: (i) The lossof time involved in entering the correspond-ing readings of the micrometer pointings on twoscales. (2) That an additional motion inter-mediate between the quick and slow motion inposition angle was necessary, because, whilst theslow m
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . read by microscopes, and the instrumentcan be used in both positions (tube precedingand following) for elimination of the effect 0Iflexure on the position angles. Elkin found thatthe chief drawbacks to speed and conveniencein working this heliometer were: (i) The lossof time involved in entering the correspond-ing readings of the micrometer pointings on twoscales. (2) That an additional motion inter-mediate between the quick and slow motion inposition angle was necessary, because, whilst theslow motion provided by Repsolds was admirablyadapted for adjusting the pointings in positionangle, it was too slow for causing the images tocross through each other in the process of measur-ing distances. To remedy drawback (i) Repsoldsdevised the form of printing micrometer which is shown in figs. I2 and13. Thismicrometer is provided with two pairs of parallel webs. Onefixed pair of webs is attached to the micromcter-Dox, the other pairis moved by the screw S. The whole micrometer-box is moved by. Fig. 12. by jerks instead of with the necessary srtioothness and the heliometer-part of Lord Lindsays heliometer was acquiredby Gill in 1879, he changed the manner of imparting the motion inquestion. A square toothed racked wheel was applied to the tubeat f (fig. 9). This wheel is acted on by a tangent screw whose bear-ings are attached to the cradle; the screw is turned by means of ahandle supported by bearings attached to the cradle, and comingwithin convenient reach of the observers hand. The tube turnssmoothly in the racked wheel, or can be damped to it at the will of
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
