( 95 ) 



ratio of the amplitudes of the first or second sound to that of the 

 third a = l, and the ratio of the frequencies 1>=2, the ratio of the 

 intensities is a 1 1? = iï>6. Hence the third sound is at its maximum 

 still about '200 times feebler than the first or second. 



While the above given figures refer to the objective intensities, a 

 comparison of the intensities of perception is still much less in favour 

 of the third sound, since a tone of frequency 50 per second has 

 objectively to be a little over a hundred times stronger l ) than a 

 tone of 100 vibrations a second, in order to produce an equally 

 strong auditory impression. Consequently, if the third sound attains 

 such an intensity that ii is just audible still, the first and second 

 sounds mav be 20.000 times weakened, before also the auditory 

 impression they produce, vanishes. 



This explains the difficulty of the investigation by the method of 

 auscultation. Gibson 2 ) emphasises this particularly and says that in 

 order to hear the sound, accidental sounds must be excluded as much 

 as possible, while one has to strain one's attention during"the interval 

 in which the sound occurs. Although the cardiophonograms leave 

 no doubt as to the existence of the third heart sound with W i, we 

 have been unable to hear it by means of a stethoscope. 



Regarding the explanation of the third sound we refer to the 

 above mentioned more extensive paper which will shortlyjbc published 

 elsewhere. Here we will only state our conclusion that the sound 

 cannot be put on a line with a prae-systolic murmur of the mitral 

 valve, nor with a duplication of the second sound by non-simultaneous 

 action of the aortal and puhnonal valves, but that it is probably 

 caused by a second vibration of the valvulae semilunares aortaeand 

 must lie regarded as a phenomenon of pretty common occurrence. 



Astronomy. - "On $omi j points in the theory of Jupiter's satellites.' 

 By Dr. W. dk Sittkk. (Communicated by Dr. E. F. van dk 

 Sande Baxhdtzen . 



The following pages contain a short account of some investigations, 

 which will soon be published, together with other results, in N°. 17 

 of the publications of the astronomical laboratory at (ironingen. 



A few words are necessary in explanation of the notations em- 



b Calculated according to Max Wiex, PilCger's Arch. f. d. gesammte Physiol. 

 Bd. 97. p. 1. 1903. H. Zwaardemaker and F. H. Quix give in Ehgelmakw's 

 Arch. f. Physiol, p. 25. 1904, differences in the same sense, but of a different 

 order of magnitude. 



*)l.c. 



