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XXir. Description of a Balance Level, iiseful for laying 

 out Land for Irrigation, for Roads, arid fur other Pur- 

 poses. By Mr. Richard Dri^w, of Great Ormond Street*. 



H, 



SIR, 



-EREwiTH y6u will receive a balance level, of my inven- 

 tion, which i have satisfactorilv used on several genllemen'^ 

 estates in Devonshire, where I have been employed to drain 

 and carry water to irrigate meadow land. I have made se- 

 veral for persons in that connty, whose employment is to 

 ^fain and irrigate land, and ihey have found it to answer 

 their purpose better than the spirit or water level, it being 

 more portable and ready to the sight. 



I have lately used it on Mr. Satterley's farm, at Hastings, 

 to carry the water of his closes over several acres of dry 

 ground. Dr. De Salis, who has seen it, advised me to send 

 it to the Society of Arts, &c., that they might judge of its 

 merits. I am, sir, your obedient servant, 



Richard Drkw. 



London, Dec. 5. 1304. 



To the Secretary of the Society ' 



of Arts, Sec. 



Explanation of the Method of using the Lislrument. 



Set it on a trianL!;ular staff, and point it at the object staff, 

 which is held by another person at a distance ; move the 

 level on the joint, until the inner tube plays clear within 

 the outer tube. Look through the sights, and observe the 

 object staff which the person holds, let him move the slide 

 on the staff until you see the hair cut the middle of the slide, 

 on which there is a black line, then turn the level round, 

 and look through the sights, you will then see if the hair 

 cuts the middle of the slide as before, which if it does, it 

 will be level, but if there be a difference in both ends, the 

 person who holds the staff must set the slide to half that 

 difference. You are then to adjust the level by turning with 



* From Transactions of the Society for the Encouragement of Arts, Ma- 

 nufactures, anc Commerce, for 1807. Ten guineas were voted to Mr. Drew, 



by the Society, for th-s communication. 



a key 



