514 



Major J. Herschel. 



taehe qu'il lui a pin de m'assigner. Vous avez ete plus sage, pour le 

 grand bien de la science. Moi, je puis malheureusement me dire, 



" ' Cras vives ! liodie jam vivere, Pc-sthume, serum est. 

 Ille sapit quisquis, Postliume, vixit heri.' — Martial." 



I have also seen a copy of the reply to this letter. It is needless to 

 say that it was full of approval, and only made some suggestions, 

 which were at once adopted or accepted. There was no mention of 

 any other form of gravimeter having been proposed in England. I 

 need not transcribe from the subsequent letters; until, on the 15th 

 February, a year later, Babinet again writes : — 



" M. Le Verrier me presse de terminer notre balance gravimetrique. 

 Je ne veux pas commencer imprudemment avant d'avoir votre ulti- 

 matum d' approbation." 



Here follows a resume of the principles involved in the design, as to 

 which I need only remark that the elasticity of the suspending wires 

 is not taken into account, nor is the necessary effect of this elasticity 

 upon the balance in any way referred to. 



" L'appareil sera etabli et essaye a l'Observatoire Imperial de Paris, 

 puis essaye dans les latitudes voisines. Je serai heureux si cette 

 mesure de lagravite et les deplacements necessaires qu'elles entrainera 

 me fournissent l'occasion de vous voir en Angleterre." 



The letter then passes on to other matters — a new plan for measur- 

 ing aberration by means of gratings — and only returns to the gravi- 

 meter at the close. 



" J'aurais encore attendu a vous parler de ceci sans la circonstance de 

 notre balance gravimetrique. En cas de succes de cette balance 

 pourriez-vous, vous ou quelqu'un des votres, vous charger des stations 

 du Royaume Uni ? II f audrait au moins une mesure de gravite pour 

 chaque degre carre de surface. 



"Nota. — Sitot apres votre reponse on se mettra a l'ceuvre pour 

 l'appareil gravimetrique. 



" Becevez, &c, 



"BABINET." 



The paper in the " Comptes Rendus " (lvi, pp. 244 — 248) was read 

 on February 9, 1863, or a week earlier than the date of this last letter, 

 which therefore appears to have resulted from the approval with which 

 the paper was received at the reading. The published account adds 

 little to what the letters tell — on the contrary — which is partly my 

 reason for transcribing them. It is noticeable that there is from first 

 to last no mention of any prior attempt in the same field. 



