VOL. LVII.3 PHILOSOPHICAL TRANSACTIONS. 405 



while that irritability is kept up by the fostering heat of the mother. This feeble 

 life is soon extinguished, when the influences of the mother's warmth and circu- 

 lation cease (No. 1.) Such infants die as soon as born, or soon after. 5. Such 

 examples, more consequentially than experiments, demonstrate that the spinal 

 marrow is the principal origin of the intercostal nerves (No. 2) ; and better than 

 ligatures illustrate their vast importance ; for, 6. From the plump state of the 

 body, and vigorous appearance of the heart, it is evident that the circulation, 

 and the developement of the several organs, had been carried on properly in the 

 foetus ; and that the irritability of the heart derived a sufficiency of nervous in- 

 fluence from the intercostal nerves, and its ganglions, and these again from the 

 spinal marrow, for growth, and that state of existence. 



Then follows the Supplement to this Author's Essay on the Use of the Gan 

 glions, which may be seen in his collected works, published in 1795. 



XF'I. Thoughts on Comets. By Mr. John fVmthrop, Profes. of Math, and 

 Philos, at Cambridge, in New England. From the Latin, p. 132. 



The scope of the following problems, is to find the limit of attraction between 

 the sun and a comet, or the point between them where a corpuscle will be equally 

 attracted by them; and also other matters depending on it. 



Prob. 1 . — Given the quantity of matter in two bodies, and the distance between 

 their centres ; to find the limit of attraction. 



In fig. 2, pi. 10, let s and c be the centres of the bodies, the greater being s; 

 and let their quantities of matter be called s and c respectively. Cut the line sc, 

 produced beyond the less body c, in a and o, so that sa may be to ac, and so to 

 oc, in the sub-duplicate ratio of s to c ; and on the diameter oa, describe the 

 semicircle ola; then the limit of attraction will be the spherical superficies 

 generated by the rotation of the semicircle ola about the axis oa. This Mr. 

 W. easily proves by the nature of the circle, since SL to lc, and sa to ac, and 

 so to oc, are all in the same ratio. 



Schol. 1. Within this limiting superficies, the force of the less body is 

 greater: without it, less. 



Corol. 1 . The diameter ao of the limiting sphere, as also its two segments ac, 

 CO, are as the distance between the centres of the bodies. — Corol. 2. Having 

 given any point in the limiting superficies, and the distance of the bodies, the 

 whole superficies will be given. — Corol. 3. From every point in this superficies, 

 the direction of gravitation is to the point a, as to a centre. For because of the 

 equality of the forces, by which the corpuscle at l is attracted towards the bodies 

 s and c, the direction of the force composed of them bisects the angle slc; 

 consequently it passes through the point a by Eucl. 3, 3. — Corol. 4. And, 

 drawing CB perpendicular to cl, meeting la in b, then that compound force will be 



