its 



TIDES. 



there is a sufficient difference of level above, and below the wheel to 

 produce the necessary head, and the sluices must be an-auged in such 

 a manner aa to regulate the dynamical effort exercised upon the whee 



T fc K, if 7 f - W rk i" g ' Which fa """fly about tours Tu 

 At other times, the motion is given by a species of horizontal 



''"^^'^^^ontallbth 



ceg 



of the wheel cannot take place con 



tinuously, for at the turn of the tide iu either cm-eetbn S is a 

 period during which it neither advance, nor recedes ; but dkectlythe 

 current assumes a marked velocity, eiUier of ebb or flow, the wheel 



ticbd ourr* \ m T "' m a ' teraate directions - A* the velocity of the 

 cUl current is always greatest about the half tides it is necisarv -to 

 provide some regulating machinery for the working^ rfSTK 

 ty should happen to be of a nature to require uniformity of 



" " ^ " * 



Th, tidal wheels attached to boats on rivers are, in fact vertical float 





.jayjs SKJ fins 



the wheels working in unlimited water, flowing in one 









semicircular form at their lower ed^esT*^?'"''!, 001 '! 1 '' 1 ''*'* * t *' e " ' * 



I 



-t of wX^ii: one M,?"^! !. 000 ^ ch '." ''"-the 

 overlaps * v 



illrll. , I., 



side 







>oa. ine nne clay M soon converted into mud at the 8iirfar V.v th- 



STit'd&teS '5 D0t r ffiC , ie f y """ t0 ' "the wat though 



air' and < ,nM f ",,' Wh ' h effsctuall y Preludes the access of 



isequently stops the vegetation of the seed. It is only by 



abundant manuring with organic matter, especially of animal orkri.f 



athnten 



- Affected it is best to stir clay soils as deep as possible by 

 ..-ploughs, but they should not be pulverised so that 

 rater cannot run down between the lumps and clods, and especi- 

 jll the surface should be left in such a 'state of roughness 'that 

 -avy runs cannot cover it with a coat of mud. The clods whicli are 

 t t on the surface imbibe the moisture more gradually, and in drying 

 leces, by which the young plants are invigorated, and, as it 

 ", moulded up. This is 1)a rticularly the case in winter after a frost, 



