239 



Id, Is it sufficiently quick to make the commencement of the 

 fall an accurate observation \ 



It is • for it falls through the first 4 feet in less than 0-3 of a 

 second ;' and as a separation of the descending ball from the fixed 

 cross staffs to the extent of 6 inches would be abundantly visible to 

 observers all over the city, they should not err to more than one 



second. , , , j 



3d, Is the impetus of this falling body sufficiently broken and 



quieted in fall, so as not to endanger the permanence of itself or 



the building'? 



The concussion is so completely broken by the cylinder of air 

 which receives and bears up the piston connected with the ball, that 

 the ball invariably comes to rest on its bed block without any sen- 

 sible shock or sound. 



4«/i, Is the dropping of so huge and cumbrous a weight as the ton- 

 heavy ball managed by a trigger sufficiently delicate to insure ex- 

 actness of manipulation, and sufficiently certain, as not to be thrown 

 out by accidental causes ? 



This is the case to an eminent degree, through the introduction of 

 a small auxiliary ball to do the labour of dropping the big one. so 

 that it is only the trigger of the small one that has to be pulled by 

 hand or by the electric force, and it has to be pulled with a force of 

 but a few grains, and through about ^'oth of an inch. 



Excepting the variations of strength of a certain spring, depend- 

 ing apparently on temperature, and now compensated by adding 

 weights each morning, no other inconvenience has been experienced. 

 And the trigger has held its place firmly, even when during some 

 of the violent gales in the winter, the top of the monument was 

 rocking about to such an extent as to make the duty of attending 

 to the ball somewhat unenviable. 



5«/i, Is there any loss of time or accuracy by the baU being on 

 Nelson's Monument, and not in the Observatory \ 



Practically, none ; for the trigger is pulled, and the ball dropped 

 by electro-magnets, which are instantaneously animated by the gal- 

 vanic circuit being completed in the Observatory. 



Uh, Is there any guarantee or permanent record of the time at 

 which the signal was, and must have been made \ 



There was not, as the ball was placed in my hands, for all the 

 exactness depended on the skill of the person making the signal ; 



