THE FARMER AT HOME. 245 



axis, and they will meet beyond the lens at a point called its focus. 

 The distance of the focus from the centre of the lens depends both 

 upon the form of the lens, and upon the refractiv3 power of the sub- 

 stance of which it is made ; in a glass lens, both sides of which are 

 equally convex, the focus is situated nearly at the centre of the sphere 

 of which the surface of the lens forms a portion ; it is at the distance, 

 therefore, of half the diameter of the sphere. The property of a lens 

 which has a double concave surface, is to disperse the rays of light. 

 Instead of converging towards the ray, which falls on the axis of the 

 lens, they will be attracted towards its thick edges, both on entering 

 and quitting it, and will, therefore, be made to diverge. Lenses 

 which have one side flat and the other convex or concave, are less 

 powerful in their refractions, than those which have been described. 

 They are called plano-convex and plano-concave. The focus of the 

 former is at the distance of the diameter of a sphere, of which the 

 convex surface of the lens forms a portion. The last kind of lens is 

 called a menis cus, being convex on one side, and concave on the 

 other, like the glass or crystal of a watch. 



LENTIL. A species of ervum. The common lentil comes from 

 France and the Valais. The thin annual root brings forth weak, 

 creeping, hairy, angular stalks, from one to two feet long, divided, 

 from near the bottom, into several branches, and clinging for support 

 to other plants ; the primate leaves stand alternately ; from the axils 

 of the leaves proceed fine stalks, which each have two or three whitish 

 flowers, hanging down. The pods do not contain more than two 

 sound seeds, flat upon both sides. Lentils are cultivated for the seeds 

 just mentioned. They require a rather sandy, yet strong soil ; they 

 are sown somewhat later than peas and vetches, because they cannot 

 endure night frosts ; they are to be sowed in drills, and well harrowed. 

 Care is to be taken that the seed is not put too deep into the ground, 

 and that the young plants are well hoed and well weeded. For the 

 harvest, the time is to be chosen when the little pods begin to turn 

 brown, though the plant may be still quite green ; and, if possible, it is 

 best to choose the afternoon of a dry, warm day ; for if the pods are 

 quite ripe, or are wet with rain at the time of gathering, they easily 

 crack open, and a great loss of seed takes place. 



Two varieties are cultivated the large garden lentil, and the 

 common field lentil. The former is distinguished by its size, and the 

 greater quantity of mealy substance which it will afford. The straw 

 of lentils is good food for cattle and sheep, particularly for calves and 

 lambs. Lentils are also mixed with vetches, and sowed as food, both 

 green and dried, for milch kine. Lentils, when cooked, afford a 

 nutritious food, (this should be done in the pod, to preserve their 

 flavor) but, like peas and beans, are not good for persons whose diges- 

 tive powers are weak, particularly if they are not cooked quite soft. 

 They ought to be boiled for two hi urs and a half. When they are 



