S74r Account of some Experiments 



same T had the first time I heard it described, that it is 

 very great. In the first place, you can he at a greater cer- 

 tainty that the teeth are all equal, llian you could be if it 

 were solid, and therefore more likely to be correct all 

 roffnd ; and, secondly, that which was by far the most 

 difficult, is by your method now rendered the easiest part 

 of the labour, namely, the racking. The framing part 

 being correctly made, and the ring well fitted on, and cor- 

 rectly steady- pinned, and the number of teeth marked in by 

 the cutter, (which may be done without that correct dividing 

 whicii is absolutely necessarv in a solid ring,) then by the 

 hcl|> of the steady pins, a blind man may finish the rack- 

 ing; and a man that can see may do it wiihoui the steady 

 pins. This I assert from practical experience, having made 

 one on your principle, and which anv person may see who 

 desires to have ocular demonstration. To sum up the 

 ivhole, yours is a self-correcting engine. 



I am, sir, 

 No. 130, Chancery- lane, Your humble servant, 



^'^"•'''''''- James Bacon. 



To Mr, Allan. 



Sir — T consider your method of racking your dividing 

 engine the best that can possibly be adopted. If carefully 

 executed, it cannot fail to produce a perfecux-ngine ; and I 

 believe it is a method that v.'ill be followed in future. 



I am, sir, 

 Ch-rles-steer, Your most humble servant, 



^"^•'=^' ''^2- Leonard Bennett. 



LXVir. An Account of some Experiments nn different Com- 

 binations qJ Fluoric Acid. By .)ohn Davy, Evr/. 

 ComuiUKicited by Sir Humphky Daw, Knt. LL.D. 

 Sec. li. .S.* 



T INTRODUCTION. 



WO years ago, I engaged, at the request of my brother, 

 Sir H. Davy, in an inquiry respecting the ixature of com- 

 mon fluoric acid >jas. My principal object was to ascer- 

 tain whether silcx is essential to its constitution, and 

 whether the proportion is constantly the same. This sub- 

 ject, and e'.perimenis on the fluoric and fluoboracic acids, 

 occupied me for about six mouths. Since that lime, the 

 work of MM. Gay Lussac and Thcnard has appeared, en- 



• From Philos. Tr.^n5. for 1S12, psrt ji. 



titled 



