58 



On Draining. 



the extent of surface which can be safely assigned to be dried by 

 a certain length of channel of a stated bore, and adapts his prac- 

 tice to the scale ; and it is obvious that if the length and distance 

 were made to exceed that correctly defined by such a rule, it 

 would be necessary to relinquish the advantages gained by the 

 . use of the small pipes. Still it might be very possible in many 

 cases to introduce such a modification as the above with utility ; 

 and as there would be at least a saving in the reduced number of 

 the junctions, perhaps with little, if any, difference of cost. 



At right angles, however, as we have supposed in the above 

 calculations, it is at least clear that the drains could not be ration- 

 ally placed ] and it may very naturally be inferred, that if we de- 

 part from that condition and arrange them at any other angle, our 

 reckonings and estimates would no longer hold good. But it 

 is a somewhat remarkable result of an investigation of this ques- 

 tion (the full explanation of which, to spare my ungeometrical 

 readers, I will consign to the modest seclusion of a note), that at 

 whatever angle these side drains are placed, — the direct distance 

 of their farthest ends from the deep ones into which they fall, and 

 the direct distance between themselves, being both fixed at any de- 

 terminate measure, — the total length of the whole series of such side 

 drains loill remain the same. This leaves us entirely at liberty to 

 select the angle of junction which we may deem most expedient 

 for other reasons. It is desirable, on the one hand, to bring their 

 lines, as far as we safely can, to approach that of the general slope, 

 but, on the other, not to make their individual lengths too great. 

 It would seem, therefore, that it could scarcely be right to make 

 their angle greater than 45°, nor less than about 20° or 30°. It 

 will be seen by the following table what are the lengths of each 

 small drain, and what the distance between their junctions in the 



Angle of 

 Junction. 



Cosecant 

 of 



Junction. 



Length 

 of Drains 

 in Yards. 



Distance 

 between 

 Junctions 

 in Yards, 



Number 

 of Drains 

 per Acre.* 



o 



45*0 



o 



1-41 



22-56 



11-28 



o 



21-4 



40-0 



1-55 



24-80 



12-40 



19-5 



35-0 



1-74 



27-84 



13-92 



17-3 



30-0 



2*00 



32-00 



16-00 



15-0 



25-0 



2-36 



37-76 



18-88 



12-8 



20-0 



2-92 



46-72 



23-36 



10-3 



* Any one may ascertain these quantities for himself upon other data, by simply 

 multiplying any chosen length and distance of the secondary drains (measured in the 

 manner already pointed out) by the value of the cosecant to any proposed angle of 

 junction ; as in the above table. 



