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Page:Popular Science Monthly Volume 89.djvu/734

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��Boring by Photography

Keeping a Deep Hole Straight

IN ALL deep borings the diamond drill (lc\iatos considerably from its- starting direction, and it is sometimes very desir- able to obtain a survey of the hole. The device here shown, which is the in\'ention of Charles B. Galvin, of Cornwall-on-Hudson, Xcw York, consists of a steel tube, ranging trom fifteen to thirty feet long, with means for indicating and recording any departure of its axis from a straight line. A geometrical straight line, tangent to the cur\ing axis of the hole, is established by the projection upon a disk of sensitized photographic paper of the image of cross-hairs etcheci on clear glass. Thus, if the hole is perfectly straight the image of the center of the cross-hairs will coincide with the center of the paper disk, and if not, the distance from the image of the center of the cross-hairs to the center of the disk rei)rescnts the amount of de\-ia- tion or rate of curvature of the hole.

The vertical and horizontal directions are established on the paper prints by means of the image of a weight, which ma\- be cither a plumb-bob or a ball, free to roll to the lowest point immediately in front of the paper. Adi.uneterdrawn through the center of the paper anil the center of the print of the ball or axis of the bob indicates the \ertical and the one at right angles to this, the horizontal. To these lines the lateral and vertical deviations respectivch' are referred. A source of light, which ma>' be a one or two-candlepower battery lamp, cur- rent for which is supplied from the surface via the cable, is situatitl in the focus of a condenser-lens. A well-defined image of the cross-hairs is thus projected on to the paper tlisk at the other end of the lube, b\' means of the objeiti\e lens which is inter|)osed at the proper focal distance between the cross-hairs and the paper. The distance from the cross-hairs to the objective would usualhbefrom two and a half to three and a half or four feet and from the objcctix'i- to the pa[)er, from twi'Ke to twent\'-live or thirl\' feet.

��Applying the photographing device to a deep bore to deter- mine whether it is straight or not. The sensitized photographic paper is at the extreme bottom of the device

���Above: A pho- tograph which represents the amount of devi- ation or rate of curvature of the hole. At left: The location and arrange- ment of the pho- tographing de- vice. The lamp is at one end of the tube and the photographic pa- per at the other


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