108 THE POPULAR SCIENCE MONTHLY 



pulse beats in the manner of Galileo, he compares it with the beats of 

 an accurate astronomical clock, which he perceives by his ear while with 

 his eye he notes the passage of the wire which supports the ball of the 

 pendulum across an accurate mark, thus being obliged to use the senses 

 of sight and hearing at the same time. He must then measure the 

 length of the wire accurately as well as the diameter of the ball which 

 hangs from it. Later on, as there will be difficulty in telling where the 

 string or wire ends, more refined means must be adopted for defining 

 and measuring its length. From the results of these measurements the 

 student will by means of theory be able to calculate the result express- 

 ing the intensity of gravity and as he presumably knows the correct 

 value, he will be under a certain temptation to so "doctor" his re- 

 sults as to make his work seem accurate. It is needless to say that such 

 doctoring can never be tolerated and is totally incompatible with the 

 character of a true scientist. The example which I have given shows 

 the nature of almost all the work that is undertaken in the physical 

 laboratory. In every experiment certain data are taken which enable 

 us to give a numerical measure of the properties of certain bodies, or a 

 statement of the numerical relations involved in phenomena. As an 

 example we may take the question of the determination of the specific 

 heat of bodies, that is to say, of the amount of heat required to heat a 

 body through a certain range of temperature. For this purpose the 

 body, say an iron ball, is heated to a certain definite temperature, let us 

 say by being immersed in the steam of a boiler in which water is boiling. 

 The ball is then dropped into a vessel containing a known quantity of 

 water and the heat that it gives out in cooling is measured by the rise in 

 temperature which the water undergoes. This apparently simple proc- 

 ess is found to be attended with a great deal of difficulty. In the first 

 place, the determination of the temperature of the ball, when in the 

 steam boiler, is no easy matter. A thermometer immersed in the steam 

 as near the ball as possible may not show exactly the temperature 

 of the ball. Secondly, if the stem of the thermometer is entirely im- 

 mersed in the hot steam the temperature shown would be different 

 from that when only, the bulb of the thermometer is in the hot steam 

 and the stem in the cool air. Thirdly, it will be difficult to transfer 

 the ball from the hot steam to the cold water so quickly that it will 

 not have lost some of its heat, which we want to measure, before it gets 

 into the water. Fourthly, as soon as the temperature of the water in the 

 calorimeter, as it is called, begins to rise the calorimeter begins to lose 

 heat by radiation to outside bodies. In order to estimate this we must 

 first study the laws of such radiation by allowing water previously 

 heated to cool in the calorimeter and observe how rapidly its tempera- 

 ture falls. Finally, it is necessary to know accurately how much water 

 was in the calorimeter, which is found by weighing, but during the 



