102 



remarkable or beautiful buildings or scenes, frequently showing the 

 presence of the photographer's friends or relations, and which form 

 pleasant reminiscences of travel. Now these constitute a branch of 

 record work, domestic records, as distinguished from those of more 

 strictly scientific and technical, that is, more general, interest. They 

 may partake of some of the qualities both of record and pictorial work, 

 but are seldom of much interest save to those concerned and their 

 friends. 



Leaving this personally interesting type out of the question, 

 those who use photography to produce results of general interest or 

 value must clearly keep in mind throughout their work the 

 fundamental differences between the two great kinds of photography, 

 which have entirely different aims, and the issues of which must not 

 be confused. 



The Graphic Solution of 

 Problems relating to the Laws of Boyle 

 and Charles. 



By Hubert Painter, b.sc, f.c.s. 



Read before the Physical Section, June 10th, igii. 



The laws mentioned in the title of my paper may be stated in 

 words as follows : — 



Law of Boyle. The volume of a given mass of gas, kept 

 at a constant temperature, is inversely proportional to the 

 pressure upon it. 



Law of Charles. The volume of a given mass of gas, 

 kept at a constant pressure, is directly proportional to its 

 absolute temperature. 



Absolute temperature is reckoned in degrees centigrade from 

 the absolute zero of temperature, which is believed to be very near 

 — 273°c. 



The usual algebraic statement of the two laws is 

 VP = RT. 



The laws only hold with mathematical accuracy for an abstrac- 

 tion known as a perfect gas, but they are very nearly true for a 

 large number of gases through a considerable range of temperatures 

 and pressures. 



In what follows I shall not deal with the departures of actual 

 gases from the laws. 



Most text-books of Chemistry and Physics give curves of two 

 kinds, called isothermal and adiabatic respectively, such curves 

 being plotted either from the results of experiments or from cal- 

 culation, but I have never met with any directions for the solution 



