l8o3' Ohfcrvatlons oiithc ConJlruEiion of Gates i8l 



part of a circle within the line of equilibrium, a Ihort pofl Is 

 placed to prevent the gate opening too near upon its equilibrium, 

 and thereby becoming liable to be left open. 



B is the upper thimble for a common gate, which is lefs ex- 

 penfive, but by no means fo good as when the it raj) extends to 

 the whole length of the gate, u'hich will be defcribeil liereafter: 

 this thimble is twilled i-4th of an inch bearing towards the 

 hanging poll. 



C is the lower thimble of a gate proportioned to the upper 

 thimble B, as i| inch is to 3 inches, in regard to the dif- 

 tance between their centres and Ihoulders refpe6tively. Thefe 

 thimbles are adapted for a gate whofe hinges are 40 inches afun- 

 der, and as 40 is to i^ the difference in this inllance, fo 

 lliould be any other diftance from hinge to hinge, to di'" propor- 

 tionate difference or extra length of the lower thimble ; and the 

 greater the e«ctra length might be made, ov«r and above fuch 

 proportion, the greater muff, become the velocity of the gate's 

 fall, or tendency towards the line of reft ; until its courfe is ar- 

 rcfted by the faitening poft i-i6thpart of the circle, or 22® 30' 

 ihort of the line of reft. The lower thimble is let into the 

 gate by a fcrew of equal fubftance throughout its lengtli, or not 

 Tapered, in order that the adjuRment of the thimbles as to the 

 velocity of the gate's fall, may be regulated to fo great a nicety 

 as half a turn of the fcrew: and the thimble may either be let 

 into the heel of the gate, or lengthened out by a wafher, ?.s occa- 

 fion ihall require. The polition of the thimbles, m rcfpecl to 

 each other, muft be favoured alfo by the lower thimble, which 

 being placed i-4th of an inch out of the middle of the heel of the 

 gate, in the contrary direftion of the upper thimbie, the whole 

 difference, as to the diftances of the two thimbles from the hang- 

 ing poft, will be one half of an inch : and their vertical plane, which 

 is the fame as that of the lines of reft and equilibrium, v.iil form 

 an angle with the line of faftening of 22° 30', or i-i6tii pa t of 

 a circle ; this adjuftment, in effedi, adds i-i2th of an inch .« the 

 extra length of the lower thimble, fo that by a plumb- " ,p, it 

 will be found (when the gate is hung upright, as it alwav.. v u;"'nt 

 to be) tliat the aftual extra lengtli of the lower thimble,'or hori, 

 zontal diftance of the two centres from each other, will be i '+. V 

 rzrl^ inch. 



D Is the upper hook. 



K is the lower hook, with keyhole and cotter, and is half an inch 

 longer from its centre to the ftioulder than the upper hook, in ov« 

 der to anfwer the thimbles ; the aclualpoiiticn of the hooks, with 

 refped to each other, or rather the horizontal didance of two per, 

 peridicular lines, one falling from the centre of each of the hoc^ks, 



will 



