[ 8a ] 



:ixis yi G in a vertical pofition, the plate <■/ wilt be kept in an 

 horizontal one, and will be a refleding level: this is efFeded by 

 fufpending the whole from a point M, (fig. 2.) in the axis, as near 

 llie plate ^ as can be, and hanging from the looped ftring /, by a 

 liook, a weight to fwing in a veffel of water, cr in the air if, it 

 be calm enough. The point of fufpenfion is in the axis of a pin 

 of fteel H* (tempered very hard) inferted through and fixed in 

 the plate B, having a conical cavity in it, whofe apex is polifhed 

 to receive the point of a ftrong and hard tempered fteel needle 

 N, which needle fupports the inftrument, and is itfelf fuftained 

 perpendicularly in an iron arm K, riveted in the plate M, by 

 which it is faftened by the fcrew L on the infide of a veffel or- 

 cafe about eight inches deep and near three inches wide inter- 

 nally : the arm K has fuch a length and pofition as that the 

 needle N fhall be in the middle of the veffel : this veffel is to 

 reft or be fuftained fteady on fome ftand, or to be fteadily faf- 

 tened by a fcrew in an upright fituation to a firm- door-pofti tree 

 or wall, &c. when the veffel is vertical its upper edges muft be 

 level, and the arm iT muft be placed fo high as that the upper- 

 furface of the plate or mirror fhall be very little higher than the 

 edges of the veffel : the lower part of the veffel is to hold water 



fufScient 



* A ftrong agate needle-cap, fuch as is ufed for compafs-needles and fixed in the 

 plate B, would anfvrer beft. 



