264 PHILOSOPHICAL TRANSACTIONS. [aNNO l/S/. 



together, and the antecedent leg placed at any other number, the other leg will 

 give its consequent in the like position or situation on the lines. If the line CD 

 happen to lie between the legs, and b be the consequent leg, the number sought 

 will be found one line farther from the centre than it would otherwise have been; 

 and, on the contrary, it will be found one line nearer in the like case, if a be 

 the consequent leg. This instrument, differing from the first only in its circular 

 form, and the advantages resulting from that form, the lines must be taken to 

 succeed each other in the same manner laterally 5^ so that numbers, which fall 

 either without or within the arrangement of circles, will be found on such lines 

 of the arrangement as would have occupied the vacant places if the succession of 

 lines had been indefinitely repeated sideways. 



Mr. N. thinks this constrL\,ction superior to every other which has yet occurred, 

 not only in point of convenience, but likewise in the probability of being better 

 executed, because small arcs may be graduated with very great accuracy, by divi- 

 sions transferred from a larger original. The circular instrument is a combina- 

 tion of the Gunter's line and the sector, with the improvements here pointed 

 out. The property of the sector may be useful in magnifying the differences of 

 the logarithms in the upper part of the line of sines, the middle of the tangents, 

 or the beginning of the versed sines. It is even possible, as mathematicians 

 will easily conceive, to draw spirals on which graduations of parts, every where 

 equal to each other, will show the ratios of those lines by means of moveable 

 radii Similar to those in this instrument. 



XXIV. Observations tending to show that the Wolf, Jackal, and Dog, are all 

 , of the same Species. By John Hunter, Esq., F. R. S. p. 253. 



The true distinction between different species of animals must ultimately be 

 gathered from their incapacity of propagating with each other an offspring 

 capable again of continuing itself by subsequent propagations: thus the horse 

 and ass beget a mule capable of copulation, but incapable of begetting or pro- 

 ducing offspring. If it be true, that the mule has been known to breed, which 

 must be allowed to be an extraordinary fact, it will by no means be sufficient to 

 determine the horse and ass to be of the same species; indeed, from the copula- 

 tion of mules being very frequent, and the circumstance of their breeding very 

 rare, I should rather attribute it to a degree of monstrosity in the organs of the 

 mule which conceived, not being those of a mixed animal, but those of the mare 

 or female ass. This is not so far-fetched an idea, when we consider that some 

 true species produce monsters, which are a mixture of both sexes, and that many 

 animals of distinct sex are incapable of breeding at all. If then we find nature 

 in its greatest perfection deviating from general principles, why may not it hap- 

 pen likewise in the production of mules, so that sometimes a mule shall breed 

 from the circumstance of its being a monster respecting mules ? 



