OF DIALING. 393 



A good meridian line, for regulating clocks or watches, LECT. 

 may be had by the following method. 



Make a round hole, almost a quarter of an inch. 

 diameter, in a thin plate of metal ; and fix the plate in 

 the top of a south window, in such a manner, that it may 

 recline from the zenith at an angle equal to the co-latitude 

 of your place, as nearly as you can guess ; for then, the 

 plate will face the sun directly at noon on the equinoc- 

 tial days. Let the sun shine freely through the hole 

 into the room ; and hang a plumb-line to the ceiling of 

 the room, at least five or six feet from the window, in 

 such a place that the sun's rays, transmitted through 

 the hole, may fall upon the line when it is noon by the 

 clock ; and having marked the said place on the ceiling, 

 take away the line. 



Having adjusted a sliding bar to a dove-tail groove, 

 in a piece of wood about 18 inches long, and fixed a 

 hook into the middle of the bar, and nailed the wood to 

 the above-mentioned place on the ceiling, parallel to the 

 side of the room in which the window is : the groove 

 and bar being towards the floor. Then, hang the 

 plumb-line upon the hook in the bar, the weight or 

 plummet reaching almost to the floor ; and the whole 

 will be prepared for farther and proper adjustment. 



This done, find the true solar time by either of the 

 two last methods, and thereby regulate your clock. 

 Then, at the moment of next noon by the clock, when 

 the sun shines, move the sliding bar in the groove until 

 the shadow of the plumb-line bisects the image of the 

 sun (made by his rays transmitted through the hole) on 

 the floor, wall, or on a white screen placed on the north 

 side of the line ; the plummet or weight at the end of 

 the line hanging freely in a pail of water placed below 

 it on the floor. But because this may not be quite cor- 

 rect for the first time, on account that the plummet will 

 not settle immediately, even in water ; it may be farther 

 corrected on the following days, by the above method, 



