Description of' an Extraordinary Parhelion. 105 



not to flow along the tube AH, the cylinder G is emptied by 

 the small aperture in its bottom, and then the can E shuts the 

 sluice. I erected a sluice of this construction in 1821, at 

 Cartsburn-mill, Greenock. The sluice is four feet long, two 

 and a half feet deep ; the lever five feet long from B to D, 

 the cylinder E sixteen inches diameter, and eighteen inches 

 deep, and filled with small stones till it weighs two hundred 

 and sixty pounds.* The cylinder G is eighteen inches deep, 

 and the same diameter. This method, wherever it can be 

 adopted, is preferable to that of Fig. 7 ; being simpler and 

 less expensive in the construction. 



Aut. XIX. — Description of an Extraordinary Parhelion 

 observed at Gotha on the 12th May, 1824. 



This very singular parhelion appeared at Gotha on the 12th 

 May, 1824, and was seen at several places around that city. 

 It was seen at Meinengen, eight leagues from Gotha, but not 

 a trace of it was observed at Bamberg, which is twenty-four 

 leagues from Gotha. 



This parhelion was observed by M. de HofF, by Dr. Buch, of 

 Frankfort, who happened to be at Gotha, and by Professor 

 Kreis. Unfortunately, however, none of these gentlemen mea- 

 sured the arches of the phenomenon with a sextant; but there is 

 reason to think that the drawing of it sent by M. de HofF to 

 Baron Zacb, which we have given in Plate II. Fig. 14. and 

 his description of it, from which we have made the following 

 abstract, are tolerably correct. This drawing was taken- at 

 half-past seven in the morning, when the apparent height of 

 the sun was 24° 51'. At this time the parhelion S'" appear- 

 ed in the horizon, so that the radius of the interior circle SS'" 

 was a little less than 24° 51'. The radius SG = SA = SB 



* The quantity of water pressing upon the sluice is twelve and a half cubic 

 feet, or 781 lbs. The pressure at the upper edge of the sluice is to that at 

 its under edge 33 8 to 22 nearly ; therefore the pivots of the sluice support 

 208 lbs. which leaves 573 to be supported by the can E ; but there is a lever 

 power of two to one, which reduces this weight one half, or to 286 lbs. The 

 weight of the lever CD itself is equal to about 30 lbs. more than the weight of 

 the empty cylinder G ; so that the whole weight of the can E requires only to 

 be 260 lbs. 



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