57 



2. On the application of the Microscope to the examination 

 of the minute phenomena of chemical action. By the 

 Rev. Edward Craig. Communicated by Dr D. B. Reid. 



Dr Reid read a notice by the Rev. Edward Craig, of some modes 

 which he had adopted for examining by the microscope, the phenome- 

 na of chemical action, by means of which, the most minute changes 

 of appearance attendant on the contact of the smallest visible quan- 

 tities of substances may be observed. The method was described to be : 



1. The laying two or more substances on two thin flat plates of glass, 

 and bringing them in contact with each other ; so that the whole mat- 

 ter is spread in one thin level between the two glasses ; and the se- 

 veral processes of union, decomposition, and crystallization may be 

 accurately watched in a field of view of yyonth of an inch. 



2. By using longer glasses which project beyond the port-object, 

 and applying a small spirit-lamp underneath, the processes of boiling 

 and evaporation may be observed. 



3. By using only one glass-plate and a lens of smaller power, so 

 that it may be raised above the vapours which would rise and con- 

 dense upon it, the galvanic battery may be applied, and its effect on 

 substances seen. 



4. By laying a thin plate of tourmaline on the port-object, beneath 

 the object to be examined, and a similar plate above the object-glass, 

 crystals may be examined microscopically in polarized light. 



These methods of observation seem to present facilities for the in- 

 cipient processes of analysis, which may be a guide to subsequent ex- 

 periments of a more measured kind. 



3. On a Register Barometer for indicating Maxima and Mini- 

 ma. By Dr Traill. 



The author gave an account of a new, easy, and economical method 

 of ascertaining the maximum and minimum of the oscillations of 

 the barometer during the absence of the observer. It consists of two 

 tubes, the diagonal and rectangular barometer of the author, fixed in 

 the same frame. A piece of thick iron wire is introduced into the upper 

 part of the former, and a similar piece into the horizontal arm of the 

 latter. These pieces of wire are pushed before the mercurial columns, 

 and when the mercury recedes, they remain behind, like the index 

 in Rutherford's thermometer. That in the diagonal barometer will 

 give the maximum, the wire in the rectangular barometer will indi- 

 cate the minimum. The portions of steel are to be replaced at the 



