LEM 



LEN 



and its back, and bearing seeds on each 

 margin of its ventral suture. 



1. Legumen Lomentaceum. A lomen- 

 tum ; a fruit differing from a legume in 

 being contracted in the spaces between 

 each seed, and there separating into dis- 

 tinct pieces. 



2. Legumin. A peculiar principle, 

 found in the fleshy cotyledons of the 

 seeds oiF papilionaceous plants. 



LEGUMINO'SiE {legumen, a legume). 

 The Pea tribe of Dicotyledonous plants. 

 Herbs with leaves alternate ; stamens peri- 

 gynous, monadelphous, or diadelphous; 

 ovarium superior, solitary, simple ; fruit 

 leguminous ; seeds without albumen. 



LEIDENFROSrS PHENOMENON. 

 If water in minute quantities be placed 

 on a red-hot plate, it will not boil, nor 

 evaporate quickly, but, as the metal be- 

 gins to cool, the liquid assumes a globular 

 figure, and exhibits a rotatory and oscil- 

 lating movement, during the continuance 

 of which the process of evaporation is 

 carried on much less rapidly than during 

 ebullition. When the metal has cooled 

 down to a still lower degree, the liquid 

 boils with great violence, and is dispersed 

 in every direction. 



LEIOTRICHA'N^. Silky chatterers ; 

 a sub-family of birds, in the system of 

 Mr. Swainson, belonging to the Ampelidce, 

 or Chatterers, and named from the genus 

 Leiothrix. 



LEMMA (XrjjUjua, any thing taken or 

 received). A proposition introduced 

 merely for the purpose of establishing 

 some more important proposition. Thus, 

 in a treatise on mechanics, if it were 

 necessary to prove certain propositions 

 of geometry, those propositions would be 

 lemmas. In Logic, a lemma is an as- 

 sumption or premiss taken for granted. 



LEMNIAN EARTH. A compound of 

 aluminum, found in the island of Lemnos. 

 It is also called sphragide {a-<ppafi?, a seal), 

 and terra sigillata, from its being cut 

 into pieces, and stamped with a seal. It 

 is similar to Armenian bole. 



LEMNI'SCATA ( Xtijui'to-Kof , a rib- 

 and). In Geometry, a curve of the 

 fourth degree, having the form of the 

 figure 8, an d of wh ich the equation is 

 x^ •\-y'^= asjx^—y^. It is the locus of 

 the point in which a tangent to an equi- 

 lateral hyperbola meets the perpendicu- 

 lar on it drawn from the centre. There 

 are many other curves of the same order 

 with a similar form, but their equations 

 differ from the above. 



LEMNI'SCUS. The Latin term for 

 194 



riband ; and, hence, applied to the minute 

 riband-shaped appendages of the genera- 

 tive pores in Entozoa. 



LEMU'RID^. A family of quadru- 

 manous animals, named lemurs which 

 supply the place of monkeys in Mada- 

 gascar and some parts of Africa and 

 India. 



LENGTH OF SHELLS. Spiral shells 

 are measured from the tip of the spire to 

 the base, and therefore perpendicularly. 

 The length of bivalves is taken horizon- 

 tally; thus, the salens is the longest 

 shell of this tribe, the length being taken 

 from the anterior to the posterior margin. 



LENS {lens, a bean). Properly, a small 

 roundish glass, shaped like a lentil, or 

 bean. In physics, the term is applied to 

 any transparent medium, the essential 

 character of which is, that it shall refract 

 the rays of light, so that the divergence, 

 or convergence, of those rays shall be 

 equally produced after their passage 

 through the lens. 



1 . The usual forms and names of lenses 

 are the convex, which converges the rays ; 

 the concave, which disperses them ; the 

 plano-convex, having one surface plane, 

 and the other convex ; the double convex, 

 having both sides convex ; the plano- 

 concave, having one surface plane, and 

 the other concave; the double concave, 

 having two concave surfaces ; and the 

 meniscus, having one side concave, and 

 the other convex. 



2. The point where no refraction is 

 produced on perpendicular rays, is called 

 the axis of the lens, which is a right line 

 passing through its centre, and perpendi- 

 cular to both its surfaces. In every beam 

 of light, the middle ray is called its 

 axis. Rays of light are said to fall di- 

 rectly upon a lens, when their axes coin- 

 cide with the axis of the lens ; otherwise 

 they are said to fall obliquely. The point 

 at which the rays of the sun are collected, 

 by passing through a lens, is called the 

 principal focus of that lens. 



3. Lens, Coddington. A well-known 

 lens, consisting of a sphere of glass 

 divided into two portions by a deeply cut 

 circular groove, which is filled up with 

 opaque matter. The lens of the cuttle- 

 fish is a precisely similar instrument. 



LENTICE'LL^. Lenticular glands, 

 or brown oval spots found upon the bark 

 of many plants, especially willows. They 

 are considered by De Candolle to bear the 

 same relation to roots as buds bear to 

 young branches. 



LENTI'CULAR {lenticula, a little 



