163 Proceedings of the British Association. 



tinual gentle circulation. While the observations were taken, 

 (1808-1811,) the building was not heated, and the lights used 

 were a few scattered tapers. It appears, that from nearly the end 

 of March to nearly the end of August, the air within the Minster 

 was colder than the mean temperature of the air without ; and 

 from nearly the end of August to nearly the end of March, 

 it was warmer. Dr. Robinson remarked, that by a slight modi- 

 fication, these observations might be made subservient to the 

 purpose of determining the rate at which the several strata of air 

 as you ascend, alter their temperatures as the conditions upon 

 which their equilibrium depend, is varied ; which determination 

 would have an important bearing on the subject of atmospheric 

 refractions. 



Prof. Lloyd communicated a paper containing the Results of 

 some investigations on the phenomena of thin plates in Polarized 

 Light. 



Prof, Wartmann, of Lausanne, read a paper on what he calls, 

 Daltonism. One of the most extraordinary affections to which 

 the eye is subject, is an incomplete vision of colors, which has 

 been called Daltonistn, after the celebrated Professor, who was 

 the first to describe it in an exact manner. He then laid before 

 the meeting, an extract from a more extended work, containing 

 in substance, the following observations. The Daltonians form 

 two classes ; — that of the dichromatics, who discern only two 

 colors, generally black and white, and who appear endowed with 

 a remarkable faculty of vision in a state of darkness : and that of 

 the poly chromatics, who have the definite perception of at least 

 three colors. Daltonism is not always hereditary; it does not, 

 even, always date from birth. Decided colors appear black to 

 many Daltonians, if they be not illuminated by a very brilhant 

 light. The number of colors of which the polychromatic Dal- 

 tonians are sensitive, is not constant ;- some only see three, others 

 four, among which blue and red may be expressly mentioned. 

 The extremes of red and violet are often not distinct ; a fact 

 which the Professor thought to have a connection with the ques- 

 tion of the number of elementary colors. The degree of polish 

 of the colored surface has an influence on the appreciation of 

 colors. Some Daltonians have an equal cognizance of the bright- 

 ness and the discoloration of siippletneniary tints, which we do 

 not recognize as such. Two colors appear to us blended by a 



