DIO 



DIO 



ubsistcnce, and both are so tame as to 

 permit any person to push them from 

 their nest, and deprive them of their eggs, 

 without the slightest resistance. The 

 hawk is perpetually vigilant for the re- 

 moval of the female, during which it darts 

 on her nest, and purloins her treasure. 

 The grey gull takes a more daring aim, 

 and assails the albatross itself, attacking 

 it beneath, to prevent which, that bird, 

 when in danger from this gull, flies im- 

 mediately to the water, and seldom leaves 

 the surface for distant flights, unless 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. 



DION.EA, in botany, a genus of the 

 Decandria Monogynia class and order. 

 Natural order of Gruinales. Essential 

 character : calyx five-leaved ; petals five ; 

 capsule one-celled, gibbous, containing 

 many seeds. There is but one species, 

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

 tive of North Carolina, in swampy places. 



DIOPHANTINE problems, are certain 

 questions relating to square and cubic 

 numbers, and to right-angled triangles, 

 &c. the nature of which were first and 

 chiefly treated of by Diophantes in his al- 

 gebra. 



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 x, y, z, are 

 expressed by rational numbers; from 

 the nature of the figure it is known that 

 x 1 -f y* = z z , where z denotes the hypo- 

 thenuse. Now it is plain that x and y 

 may also be so taken, that -z shall be 

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



Now the art of resolving such prob- 

 lems consists in ordering the unknown 

 quantity or quantities in such a manner, 

 that the square or higher power may 

 vanish out of the equation, and then, by 

 means of the unknown quantity in its 

 first dimension, the equation may be re- 

 solved without having recourse to incom- 

 mensurables. e- g. let it be supposed to 

 find x, y, z, the sides of a right-angled tri- 

 angle, such as will give x l -\-y*=-z*. Sup- 

 pose z=x-\-u, then x 3 --^-y 1 =x 1 +2 X# 

 4-w 2 ; out of which equation x* vanishes, 



_tt 

 and* =. - : then assuming!/ and u 



equal to any numbers at pleasure, the 

 sides of the triangle will be y, y * X u * 



and the hypothenuse x -f- ~ y XM * . if 



y = 3, and u 



4, and 



x+u= 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- 

 tennae. There are three species, viz. D. 

 ichneumonea, which resembles the ich- 

 neumon, and is found in Guinea. D. ni- 

 gra, described by Illiger, found on the 

 coast of Sierre 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 inseets 1 we had the good for- 

 tune to discover, early in the month of 

 May last, on the banks of the Wissahickon, 

 within a few 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, membranaceotis. 

 There are fifteen species. These plants 

 have usually tuberous perennial roots, 

 with twining stems from right to left; 

 flowers axillary, in spikes or racemes, 

 Several of these species are natives of the 

 East and West Indies, where they are 

 cultivated for food. 



DIO S MA, in botany, a genus of the 

 Pentandria Monogyriia class and order. 

 Natural order of Aggregate. Rutacex, 

 Jussieu. Essential character: corolla 



