228 LECTURES TO SCIENCE TEACHERS. 



and animals ; the application of instruments of measure- 

 ment to the investigation of the electrical and other 

 changes which present themselves among the physiological 

 effects of excitation of nerves and muscles ; and, finally, ike 

 application of recording instruments to tJie investigation of the 

 movements of living beings. Each of these applications has 

 great names associated with it the names of the men, all 

 of them now living, who, some thirty years ago, began the 

 great work of building up physiology on an entirely new 

 foundation. Among the microscopists may be named 

 Henle, Kolliker, Bowman ; of vital physicists, Helmholtz, 

 Donders, Briicke, Du Bois Reymond, and lasi^ but not least, 

 Ludwig. 



It was by Ludwig that the method of investigation, of 

 which I have to give you some illustrations to-day, was 

 introduced. He invented and constructed the first registra- 

 tion apparatus somewhere about 1846. Before I describe it 

 to you, I must explain the meaning of the term. 



Let me then first state that registration, in physiology, 

 means the obtaining of a written line or tracing whieh 

 shall exhibit the position of a moving body at every 

 moment of time during the period of observation. The 

 method by which this is effected is called the graphic 

 method. 



It follows from this definition that the motion to be 

 recorded must be a linear motion, i.e., a motion along a 

 given line. I can best explain this by proceeding at once 

 to examples. 



Suppose that I wish to inscribe graphically on this sheet 

 of paper the motion of a train travelling between South 

 Kensington and Queen's Road, 1 how would I attempt to do 

 it 1 I make my sheet of paper rectangular, for I have two 

 processes to record simultaneously, which, for the moment, 

 I conceive of as going on in directions at right angles to 

 each other, one of which, viz., time, is uniform, the other, 

 viz., the motion of the train, is variable. My purpose is 

 to compare the variable with the uniform, i.e., to record 

 motion in relation to time. 



I begin by marking off against the side of my paper the 

 whole distance in miles from one end of the line to the 



Names of stations on the Metropolitan Kailway. 



