914 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



obtained, the greatest strength of chemical action would take 

 place. As all rays reflected, whether of light, heat or chemical 

 action, are at right angles from the plane from which the reflection 

 takes place, Mr. W. used a concave mirror instead of a lens, 

 thereby not only doing away with the chief difficulty, but produc- 

 ing the result in a much shorter time. We have seen a number 

 of minatures taken from life with this instrument, which are most 

 strikino: resemblances of the oriijmals. We cannot leave this sub- 

 ject without recording our humble opinion that Mr. W.'s improve- 

 ment does himself and his country infinite credit. We received 

 the following letter from Mr. Wolcott a few days since, which 

 will fully explain his method : 



New York, March IWi, 1840. 



Dear Sir — When the announcement Avas first made of M. 

 Daguerre's method of imprinting the beautiful images of the 

 camera on silver plates, the remark was very generally made, that 

 taking likenesses from life would be one of the most important 

 uses to which it could be applied. 



On reflection, it appears that on account of the difficulty of a 

 person's remaining perfectly still for any great length of time, 

 without the appearance of constraint, or without changing the 

 expression of the face, the great desideratum was to construct a 

 camera that should condense the greatest quantity of light to form 

 the image that was consistent with distinctness. Not having an 

 achromatic glass in my possession larger than the object glass of 

 a microscope, I proceeded to experiment Avith a single concave 

 reflector, as the most simple of all optical instruments, and as the 

 one which, if of large dimensions and truly elliptical, would most 

 probably best answer the above ends of distinctness and brilliancy 

 combined. 



My first experiment was, I think, in October, with a reflector 

 of 1^ inches dperture and 2 inches focus. With this I took the 

 profile of a person standing opposite a window; and here having 

 but the three principal facts relating to M. Daguerre's process, 

 viz: The exposing the plates to vapor of iodine, afterwards to 

 that of mercury, and the washing in hyposulphate of soda, or in 

 common salt, I fell into the same error as probably many others, 

 which was, that I supposed it necessary to keep the plate in the 

 camera until the image was visible. 



This error prevented my making a larger instrument imme- 

 diately; that which I now use is 7 inches clear aperture, and is 



