VAR 



VAR 



The regular variations occur almost 

 always at the same time of day, attain- 

 ing daily two minima and two maxima. 

 They show that an ebb and a flow take 

 place in the atmosphere, similar to what 

 is observed in the sea. These are very 

 small, the oscillation seldom amounting 

 to more than a line, and are, for the most 

 part, observable only in the torrid zone. 

 The irregular changes are much greater 

 in degree than the regular, and are more 

 frequent and observable as we approach 

 the poles ; for this reason less notice is 

 paid by us to the regular alterations in 

 the height of the mercury. 



VARIATIONS, CALCULUS OF. 

 " When a quantity is subject to one sort 

 of variation only, the consideration of 

 that variation belongs to the simple dif- 

 ferential calculus; but when it is sub- 

 ject to two or more distinct sorts of vari- 

 ation, suppose that of the differential cal- 

 culus and another, then the mode of deal- 

 ing with the second sort of variation 

 is said to belong to the calculus of vari- 

 ations." 



Illustration. "In Dynamics, for ex- 

 ample, there are two distinct species of 

 motion to consider : one which, at the 

 end of the time t, the system is about to 

 take during the ensuing time dt in con- 

 sequence of the velocities acquired by its 

 particles ; and another which, without 

 any consideration of the first, must be 

 impressed upon it for the examination of 

 the conditions which express the equi- 

 valence of the impressed and effective 

 forces. Here then is a case for the cal- 

 culus of variations." — Pen. Cycl. 



VARIATIONS, PERIODIC and SE- 

 CULAR. In the language of Astronomy, 

 the term variation denotes a change of 

 inclination of the orbit of a planet occa- 

 sioned by a disturbing body. When these 

 changes are compensated by the configu- 

 rations of the disturbed and the disturb- 

 ing body with each other, and therefore 

 in comparatively short periods, they are 

 called periodic variations ; and the devi- 

 ations, thus compensated, are called in- 

 equalities depending on configurations. 

 When the compensation is operated by a 

 period of the node, it has nothing to do 

 with the configurations of the bodies, but 

 requires an immense period of time for 

 its consummation, and is, therefore, dis- 

 tinguished from the former by the term 

 secular variation. 



The variation of the moon is an in- 

 equality of the moon's motion, depending 

 on the angular distance of this body from 

 359 



the sun. It arises from that part of the 

 sun's disturbing force which is at right 

 angles to the radius vector, and which 

 accelerates the motion of the moon from 

 the quadratures to the syzygies, and re- 

 tards it from the syzygies to the quadra- 

 tures. 



VARIEGATION IN PLANTS. A 

 general term denoting the arrangement 

 of two or more colours in the leaves, 

 petals, and other parts of plants. These 

 parts are said to be marbled, when a sur- 

 face is traversed by irregular veins of 

 colour, like a block of marble ; discoidal, 

 when there is a single large spot of colour 

 in the centre of some other colour ; ocel- 

 lated, when a broad spot of some colour 

 has another spot of a different colour 

 within it, like a little eye; tessellated, 

 when the colours are disposed in small 

 squares, like those of a tessellated pave- 

 ment ; lettered, when the spots of colour 

 present the form and appearance of 

 letters. Other terms are employed of 

 more common use, and requiring no ex- 

 planation, as striped, dotted, banded, &c. 



VARIETIES. In Botany, varieties of 

 plants are individuals subordinate to spe- 

 cies. The variety differs from the species 

 in points of structure which are de- 

 veloped only under particular circum- 

 stances, and which are not essential to 

 the species. The characters on which a 

 species is founded should be invariable 

 under all circumstances ; the characters 

 of a variety are induced by local situa- 

 tion, by atmospheric influence, by culti- 

 vation, &c. ; with all the characters of the 

 species, the variety may differ in a change 

 of colour, an increased number of petals, 

 &c. Varieties may be subdivided, with 

 reference to other non-essential points, 

 constituting sub-varieties. The term va- 

 riety is similarly employed in Zoology, 



VA'RIOLITE. A porphyritic rock 

 consisting of an imperfectly crystallized 

 aggregate of felspar and quartz. 



VARIX. A swollen vein ; a term em- 

 ployed in Malacology to denote the strong 

 elevated ridges which cross the whorls of 

 several of the predaceous genera, as mu- 

 rex, triton, &c. ; they mark the progres- 

 sive enlargement of the shell, being the 

 remnants of former apertures, beyond 

 which the animal, when grown, forms 

 another aperture. 



VARNISH. A substance made by 

 dissolving resins in alcohol, or oil of tur- 

 pentine, or in a mixture of oil of turpen- 

 tine and a drying oil. There are alcoholic 

 or spirit varnishes, volatile-oil varnishes, 



