40 • REPORT — 1841. 



The translation of a given number into the ternary combination of signs suited to 

 express it, requires the aid of voluminous tables, which may perhaps be simplified. 



In the machine, the successive rods have the power of the number that would be 

 expressed by a +, or — , or 0, in the place in which the brass nail appears. The 

 range of the machine is greatly extended by the use of the lines parallel to the zero 

 line, for thus 3 +'s or 4 — 's may be in succession placed by the rod being carried 

 down 3 lines or up 3 lines, and thus additions and subtractions are performed by the 

 very motions which work the rods in the processes of multiphcation and division. 

 The extent of power of the machine will be conceived if we consider that 7 +'s fol- 

 lowed by 480 can be set on the machine, and would represent the number 



87104955839944780770790212; 

 while 55 +'s would be, if all the rods were set one line only below the zero, 



87224605504560089535585253, or 

 87 quadrillions, 224605 trillions, 504560 billions, 89535 millions, 585253 thousands. 



Letter from Sir John F. W. Herschel, dated July 31, 1841. 



Sir, — Allow me to requ'est that you will submit to the inspection of the Physical 

 Section of the British Association the annexed specimens (fifteen in number) of 

 coloured Photographic copies of engravings and mezzotintos, into the preparation of 

 which no metallic ingredient enters, the whole being tinted with substances of vege- 

 table origin variously prepared. 



The rays of the spectrum which have eaten away the lights in these Photographs, 

 are neither the so-called chemical rays beyond the violet, nor the calorific rays be- 

 yond the red. The action is confined almost entirely to the luminous rays, and of 

 these more especially to those rays of the spectrum whose colour is most contrasted 

 with, or which enter most sparingly into, the composition of the ground tint ; 

 a circumstance which, considering the great command of colour which this new 

 variety of the photographic art affords, holds out no slight hope of a solution 

 of the problem of a photographic representation of natural objects in their proper 

 colours. 



Unwilling to occupy the time of the Section so near its conclusion, I pretermit 

 for the present all details of manipulation, and remain. 



Sir, yours very obediently, 

 J. F. W. Herschel. 



On Daltonism, By Professor Elie Wartmann of Lausanne. 



Of all the organs of sense with which man has been provided, none is more deli- 

 cate than that of vision : it is subject also to a great number of affections, the study 

 of which is important in the highest degree both to the physicist and to the physio- 

 logist. One of the most remarkable of these affections is an incomplete vision of 

 colourp, which has been called Daltonism, from the name of the illustrious philoso- 

 pher of Manchester, who first described it in an exact manner. 



As the various treatises and scientific collections contain merely scattered data on 

 this peculiarity of vision, it appeared to me that it would be interesting to collect together 

 all the authentic materials for its history which have hitherto been pubhshed, for the 

 purpose of comparing them with the results of new observations, and of being en- 

 abled, finally, to assign a common origin to all the varieties of this disease of vision. 

 1 extract from a work of considerable extent the following conclusions, which appear 

 to me to generalize the known facts on the subject, and to agree with others which 

 still remain unpublished. 



1. There are two distinct classes of Dalf onions, viz. the dichromatic, who can only 

 discern two colours, commonly black and white, and who appear to be endowed 

 with a remarkable faculty of seeing in comparative darkness ; and the polychromatic, 

 composed of individuals who perceive at least three colours normally. 



2. Daltonism is not always an hereditary affection, nor does it always date from 

 the birth. It appears in certain infants born of parents who possess ordinary vision, 

 and independently of the order of birth and of sex. 



3. Deep colours appear black to many of these persons, unless they are illuminated 

 by a bright light. 



4. The number of colours perceived in the spectrum by polychromatic Daltonians 



