mo 



DIG 



subsistence, and both arc so tame as to 

 permit any person to push tlic-m from 

 their nest, ami deprive them of theiregts, 

 without the slightest resistance. The 

 hawk is perpetually vigilant for the re- 

 moval of the female, (luring' which it 

 darts on her nest, and purloins her trea- 

 sure. The grey gull takes a more daring 

 aim, and assails the albatross itself, at- 

 tacking 1 it beneath, to prevent which, that 

 bird, when in danger from this gull, flies 

 immediately to the water, and seldom 

 leaves the surface for distant flights, un- 

 less in the seasons of its migration. The 

 nests of the albatross, when vacated by 

 them, are immediately occupied by the 

 penguin. Albatrosses have been seen by 

 voyagers at the distance of 600 leagues 

 from land. For the albatross, see AVES, 

 Plate VI. fig. 3. 



DIONJEA, in botany, a genus of the 

 Decandria Monogynia class and order. 

 Natural order of Gruinales. Essential 

 character : calyx five-leaved ; petals five ; 

 upsulc one-celled, gibbous, containing 

 many seeds. There is but one species, 

 viz. D. mucipiila, Venus's fly-trap, a na- 

 tive of North Carolina, in swampy places. 



D10PHANTINE problems, are certain 

 questions relating to square and cubic 

 numbers, and to right-angled triangles, 

 8tc. the nature of which were first and 

 chiefly treated of by Diophantes in his 

 algebra. 



In these questions it is chiefly intended 

 to find commensurable numbers to an- 

 swer indeterminate problems; which of- 

 ten bring out an infinite number of in- 

 commensurable quantities. For example, 

 let it be proposed to find a right-angled 

 triangle, whose three sides .r, y, :, are ex- 

 ed by rational numbers; from the 

 nature of the figure it is known that 

 .r 1 -|- y- = ;\ where : denotes the hypo- 

 \ow it is plain that .c and \j 

 may also be so taken, that : shall be 

 irrational ; for if a- = 1, and y = 2, then is 

 .- = y 5. 



Viv, tin* art of resolving such pro- 

 blems consists in ordering the unknown 

 quau'.'.'y '! >u such a manner, 



that llu- square or higher power may 

 vanish <>'r, of the equation, and then by 

 means of the unknown quantity in its 

 first dimension, the equation may be re- 

 solved without having recourse toincom- 

 melisii;:''les. c. if. let it be supposed to 

 I' -.of a right angled tri- 

 angle, sm'li as will give .r--\~u-=:z-. Sup- 

 .,--+- i/, then .r'-f- /'= .r'-f- 2x 

 -f M 1 j out of which equation .r- vanishes, 



and x = 







: then assuming y and u 



equal to any numbers at pleasure, the 



jy4 1^ ,..! 



sides of the triangle u ill be v, jr 9 



and the hypothenuse x -f- = - y^- ; if 



*& zi 



M It'- 

 ll =3, and ?< = 1, then = 4,and 



2 v 



o--4-j/=5. It is evident that this problem 

 admits of an infinite number of solutions. 



DIOPSIS, in natural history, a genus 

 of insects of the order Diptera. Generic 

 character: head with two inarticulate 

 filiform horns, bearing the eyes and an- 

 tennse. There are three species, viz. D. 

 ichneumonea, which resembles the ich- 

 neumon, and is found in Guinea. D. 

 nigra, described by Illiger, found on the 

 coast of Sierra Leone. D. brevicornis, pe- 

 duncles of the eyes not longer than the 

 distance between their bases, they are 

 brown ; head, posterior spines and feet 

 pale yellow ; poisers white ; thorax fus- 

 cous; lateral spines and abdomen black; 

 fore thighs much thickened, with the 

 shanks brown, and pale yellow joints; 

 wings fasciated near the apex. 



The last species of this truly singular 

 genus of insects we had the good for- 

 tune to discover early in the month of 

 May last on the banks of the Wissahickon, 

 within afew miles of Philadelphia; it had 

 perched upon the leaf of the swamp cab- 

 bage (Pothos Foetida) and is now in the 

 collection of the writer of this article. 



DIOPTRICS, the science of refractive 

 vision, or that part of optics which con- 

 siders the different refractions of light in 

 its passing through different mediums, as 

 air, water, glass, &c. and especially len- 

 ses. See OPTICS. 



DIOSCOREA, in botany, English yam, 

 a genus of the Dioecia Hexandria class 

 and order. Natural order of Sarmenta- 

 cex. Asparagi, Jussieu. Essential charac- 

 ter : male, calyx six-parted; corolla none. 

 Female, calyx six-parted ; corolla none ; 

 styles three; capsule three-celled, com- 

 pressed; seeds two, membranaceou*. 

 There are fifteen species. These plants 

 have usually tuberous perennial roots, 

 \\ ith twining stems from right to left ; 

 flowers axillary, in spikes or racemes. 

 Several of these species are natives of the 

 East and AVest Indies, where they are 

 cultivated for food. 



D1OSMA, in botany, a genus of the 



.dm Monogynia class and order. 



Natural order of Aggregate. Rutacesc, 



Jussieu. Essential character . corolla 



