FREE BOOKS

Author's List




PREV.   NEXT  
|<   15   16   17   18   19   20   21   22   23   24   25   26   27   28   29   30   31   32   33   34   35   36   37   38   39  
>>  
quite off the dial at _c_, or 3 o'clock in the afternoon; at this time the shadow of the corner _i_ will appear on the side _h g_ at _q_ or 3 o'clock, where place the figure 3; the shadow will then ascend to _p_ at 4, to _o_ at 5; at 6 there will be no shadow, the sun shining right along the line _i h_; place a VI also at the corner _l_, because it also shines along the line _l k_, and from 6 till 9, (if it be in a latitude where the sun continues up so late) the shadow of the corner at _k_ is passing along the line _l m_: therefore take the distances _h o_, &c., and set off from 6 to 7 and from 6 to 8, as before at 12, 1, and 2. Then for the morning hours, the shadow of the corner _c_ will enter upon the line _a b_ at the point _a_, just at 3 o'clock in the morning, and if you draw lines from 7 and 8 parallel to _a m_, their terminations will point out 4 and 5. Six o'clock is in the very corner opposite to 6 in the evening. Parallel lines below the transverse piece drawn from 5, 4, 3, will indicate the proper places for 7, 8, 9. It then remains to set off the same distances as before on line _l k_ on which the shadow of _m_ will point out 11, 10, and 9 o'clock; the dial will then be finished. _Observe._ These dials require considerable thickness (_let it be equal to a m_,) because being placed parallel to the equator, the sun shines upon the upper face till the summer, and on the longest day is elevated 23 deg. 29' above the plane of the dial, and consequently the shadow of _a_ will fall at noon in the line _a b_, not in the point _b_, but at an angle of 23 deg. 29' therewith, and on the shortest day the like angle will be formed, but in an opposite direction. It must further be observed that after the proper points are determined on the plane, they had better be transferred to the sides of the cross, as is shown in _fig._ 2, for there it is the shadow will be seen to pass. A dial thus formed is universal; when made according to the foregoing directions there is nothing more to do but to fix it by the help of your quadrant to the elevation of the equinoctial or complement of the latitude of your habitation, and so that the side _a m_ may exactly face the south. A dial of this sort has been standing in my garden, more than 12 months, and is found to answer the purpose well, being both useful and ornamental. When the figures are painted on the thickness as in _fig._ 2, the upper surface being unoccupied, an equinocti
PREV.   NEXT  
|<   15   16   17   18   19   20   21   22   23   24   25   26   27   28   29   30   31   32   33   34   35   36   37   38   39  
>>  



Top keywords:

shadow

 
corner
 

morning

 
parallel
 

thickness

 

opposite

 
formed
 

proper

 

latitude

 

distances


shines

 
universal
 

afternoon

 

directions

 

foregoing

 

transferred

 

points

 
determined
 

observed

 

quadrant


purpose

 

answer

 

months

 

ornamental

 

unoccupied

 
equinocti
 
surface
 

painted

 
figures
 

garden


elevation
 

equinoctial

 

complement

 

habitation

 
standing
 

transverse

 

Parallel

 

evening

 
remains
 

places


terminations

 
passing
 

continues

 

figure

 

ascend

 
elevated
 

shortest

 
therewith
 

longest

 

summer