172 



Improved Agricultural Drainage Level. 



screw in the upper one c. The contrary when the line of sight 

 points too low ; move the screws only a little at a time, and take 

 care not to force them too tight. Repeat this until the horizontal 

 line of the telescope intersects the staff at the proper place ; in 

 this example, at 56^ inches. 



Another method to make this adjustment is by means of a 

 sheet of water, which, when it can be come at sufficiently large, 

 is convenient and accurate. At the distance of about 40 yards, 

 drive two stakes close to the water's edge, till the upper ends 

 are even with the surface of the water ; fix the level over one of 

 the stakes, and the staff perpendicularly upon the other; adjust 

 the instrument for reading the staff, then measure the height of 

 centre of object glass above the stake over which it is placed. If 

 the reading of the staff is not the same, make it so, by moving the 

 horizontal line up or down by the collimation screws, cc. 



This is an adjustment, when once well made, that seldom re- 

 quires repeating. 



The Levelling Staff — to accompany the level, is made of ma- 

 hogany, well seasoned ; light and portable. Its length when closed 

 is five feet, when drawn out, 9^ feet. It is divided into inches 

 by strong black lines, upon a white ground, which can be easily 

 read through the telescope of the level, at the distance of 100 

 yards. 



Price of the new Drainage Level improved, with book of instruc- 

 tions for using it, SI. bs. — Price of Staff, above described, 15s. 



VIII. — On Hemp. By Thomas Rowlandsox. 



Hemp (Cannabis Sativa of Linnaeus) belongs to the same order 

 of plants (Diascia Pentandria) as the well-known plant which 

 grows on dry ditch and hedgerow sides — the common stinging- 

 nettle, which in outward appearance it greatly resembles. The 

 common nettle has repeatedly been used economically in the ma- 

 nufacture of textile fabrics. 



The soil best suited to the growth of hemp is a deep, rich, 

 alluvial, and moist, mellow mould; one in which well- decomposed 

 vegetable matter is mixed with alluvium composed of fine clay 

 and sand, and intimately mixed, I have found the best adapted 

 to its cultivation. Rich old pasture land fresh broken up, if not too 

 stiff, is the soil on which hemp particularly luxuriates. On such 

 pastures being broken up, which may be deemed too rich for flax, 

 and on which the cereals would run too much to straw, hemp can 

 be grown with the greatest advantage. Hemp is a plant of exceed- 

 ingly rapid growth when grown under favourable circumstances, 



