318 Mr. A. H. Garrod on the relation of the Cardiograph [Feb. 23, 



It was found that from ten to twelve Fraunhofer lines could be regis- 

 tered in about 15 seconds, and that, when the same lines were recorded five 

 times in succession on the same card, no sensible difference of position 

 could be detected between the pricks registering the same line in the 

 several spectra. 



It is obvious that, by registering the spectra of different substances on 

 the card, a ready method is obtained of comparing the relative positions 

 of the lines of their spectra. 



Each spectroscope was furnished with a compound prism, which was made 

 by Mr. Grubb, and gave a dispersion equal to about two prisms of dense 

 glass with a refracting angle of 60°. 



Postscript. — I have just learned that in a spectroscope contrived by 

 Professor Winlock for observing the eclipse of December 22, 1870, the 

 positions of the observing-telescope are registered by marks made upon a 

 plate of silvered copper. — February 3, 1870. 



February 23, 1871. 



WILLIAM SPOTTISWOODE, M.A., Treasurer and Vice-President, 



in the Chair. 



The following communications were read : — 



I. "On the Mutual Relations of the Apex Cardiograph and the Radial 

 Sphygmograph Trace." By A. H. Garrod, of St. John's 

 College, Cambridge. Communicated by Dr. Garrod. Received 

 January 18, 1871. 



A desire to acquire an accurate knowledge of the relation borne by the 

 commencing contraction of the heart to the origin of the primary rise in 

 the pulse at the wrist, led the author to construct an instrument which 

 has enabled him to determine, with considerable accuracy, the mutual 

 relation of these two points, and to demonstrate one or two unexpected 

 results, not altogether without interest. 



The cardio-sphygmograph above mentioned consists of a piece of board, 

 10 inches long by 5| inches broad, and about half an inch thick, along one 

 side of which a sphygmograph can be laid, as shown in fig. 1 . On the 

 opposite side a spring (a) like that employed in the sphygmograph is 

 attached to a moveable support (b), so that its tension can be modified. 

 To the free end of the spring a small pad (c) is fixed, which is in com- 

 munication with the cardiograph apparatus by means of a silk thread (d). 

 This latter instrument consists of a light lever (e), a little over 2 inches 

 long, connected to the board first mentioned by a frame (/) which is just 

 free from the sphygmograph when the latter is in position. The lever, 

 which is one of the third system, is connected on either side, close to its 



