May 14, 1891] 



NATURE 



35 



be represented by lifting the chain with a weak thread, 

 and by having the end of the chain fastened to a pretty 

 strong spring. When the thread broke the spring 

 would pull the chain back quickly, would pass its 

 position of equilibrium, and thus commence a series 

 of rapid vibrations on each side of this position ; 

 the vibrations would gradually die away owing to 

 the energy of the spring being gradually spent, partly 

 on friction in itself, and partly in sending waves 

 along the chain. In actually performing the experiment, 

 an india-rubber tube or limp thin rope is better than a 

 chain when hung horizontally, as the chain is so heavy ; 

 when it can be hung vertically, a chain does very well. 

 I n the description it simplifies matters to describe a chain, 

 because it is easier to talk of a link than of a bit of the 

 rope : a link has an individuality that identifies it, while 

 a bit of the rope is so indefinite that it is not so easy to 

 keep in mind any particular bit. Consider now what 

 these waves are, what sort of motion originates them. 

 When the spring first starts, the near parts of the chain 

 move first. What happens to any, link ? One end of it 

 moves down before the other. What sort of motion, 

 then, has the link ? It must be rotating. Thus it is that 

 change in the displacement is generally accompanied by 

 rotation of the links. Thus it is that change in electric 

 strain is accompanied by magnetic strain. The analogy 

 goes farther than this. Each wave thrown off may be 

 described as a wave of displaced or as a wave of rotating 

 links, and the most displaced are at any time the mobt 

 rapidly rotating links. Just in the same way, what have 

 hitherto been called waves of electric force may also be 

 looked upon as waves of magnetic force. Because there 

 are two aspects in which the motion of the chain may be 

 viewed does not diminish from the essential unity of 

 character of the wave-motion in its waves ; and similarly 

 the fact that these Hertzian waves have an electric and a 

 magnetic aspect does not diminish from the essential unity 

 of character of the wave-motion in them. At the same 

 time the two elements, the displacement of a link and the 

 rotation of a link, are quite distinct things ; either might 

 exist without the other ; it is only in wave propagation 

 that they essentially co-exist. In the same way electric 

 strain and magnetic strain are quite different things ; 

 though in wave-motion, and indeed whenever energy is 

 transmitted from one place to another by means of the 

 eth^, they essentially co-exist. 



FIVE YEARS' PULSE CURVES. 



/^VER five years ago it occurred to me that there would 

 ^-^ be considerable interest in keeping a systematic 

 record for some time of the rate of pulsation, i.e. of the 

 number of beats (per minute) of the pulse. I therefore 

 commenced the practice by taking, every night, an obser- 

 vation of my own pulse ; these observations, originally 

 undertaken solely for my own personal interest, have 

 been continued without intermission up to the present 

 time ; and, on throwing the results into a graphic form, I 

 found so close a symmetry and concord between the curves 

 for these five years, that I thought it might be interesting 

 to readers of Nature to have these results put before 

 them. 



First, then, as to the method adopted in these observa- 

 vations. I count the pulse beats for one minute ' every 

 night ' before retiring to bed, and invariably while in a 

 standing posture. From the records thus obtained the 

 average for each month is deduced in the usual way, viz. 

 by adding together all the numbers for the month, and 

 dividing by the number of days on which observations 

 were taken. With regard to this important consideration 



' Thus avoidingtthe considerable error that is introduced by counting for, 



y, fifteen seconds only, and multiplying. 



^ The time has varied from 23.0 o'clock to i o'clock. 



NO. I 124, VOL. 44] 



— i.e. of the number of observations, since an insufficiency 

 thereof would, of course, greatly vitiate the value of my 

 curves — I may state that during the first four years I 

 omitted to take an observation on only seventeen nights 

 altogether. During the fifth year, I find twenty-one ob- 

 servations missed. Nevertheless, the net data from 

 which the curves are deduced are not quite so abundant 

 as this statement would imply ; for, in calculating the 

 monthly average, I have invariably struck out altogether 

 all readings above 79. My reason for this procedure 

 was simply that I wished to obtain a curve showing the 

 normal pulsations ; now, anything much above 75 is 

 abnormally high (especially in my own individual instance, 

 for it will be noticed that my pulse is below the usual 

 average of 70), and I can nearly always assign a distinct 

 cause, such as the feverishness caused by a cold, or 

 excitement, or recent exercise ; it therefore appeared to 

 me fairest to knock out altogether the results of such 

 disturbing causes, and since for this purpose an arbitrarj' 

 line must be drawn somewhere, I decided to draw it at 

 79. On the other hand, however, I have retained all the 

 other readings, no matter how low they might be, although 

 the " fifties " are very common, and occasionally even the 

 "forties" have been touched. It might, perhaps, be 

 thought that these very low readings should be neglected 

 equally with the very high, but such a course appeared to 

 me altogether illegimate, both because such low readings 

 seemed, judging from their occurrence, to be, so to speak, 

 normally caused, and unassignable to any distinct extra- 

 ordinary cause known to myself, and also because I 

 should hardly have known where to draw a minimum 

 line. However, I now regret that the readings below 50, 

 at any rate, were not rejected ; but such readings are so 

 extremely rare that they cannot have much influenced 

 the curves. In order that the reader may judge for 

 himself on what data these curves are founded, I have 

 appended a table showing the net number of readings 

 from which each monthly average was drawn, and have 

 also stated (in brackets) the number of readings below 

 60 included in each month. 



Turning now to the curves themselves, this monthly 

 average is shown by Xht'thin line. It is necessary to 

 explain that these curves were drawn by marking the 

 monthly average by a dot on the extreme right of each 

 space representing a month. I was undecided for some 

 time whether to adopt this plan or to mark this dot in 

 the middle of each monthly space ; but after trying both 

 plans I concluded that now adopted to be the simpler. 

 The actual curves were, of course, obtained by connecting 

 all these dots by straight lines. 



On examining this mojithly curve, it is at once obvious 

 that there is a strong similarity between the five years ; 

 clearly every year the curve falls through the spring, until 

 about midsummer, and then rises wonderfully steadily 

 and regularly in every case (except in 1889) through the 

 autumn to November or December. On the whole, two 

 maxima seem to be indicated — namely, one in Nov- 

 ember, followed by a fall, and then by a rise to another 

 maximum in February or January. But it will be noticed 

 that in the winter 1889-90 there is the unusual pheno- 

 menon of a fall through November, and then the two 

 maxima are replaced by an intermediate maximum 

 reached in December. So that here, in spite of the 

 broad concord and regularity, there was rather too much 

 local irregularity to be altogether satisfactory. In the lower 

 portions of the curves, again, there is even more irregu- 

 larity. Those of 1887 and 1888 (but emphatically the 

 former) are indeed remarkably free from aberration ; but 

 in 1886 there is an extraordinarily abrupt and irregular 

 rise through July, followed by a compensating fall 

 through August. In 1890 there is an almost identical 

 irregularity in the same two months; while in 1889 we 

 have a remarkable irregularity in the spring. Now these 

 irregularities puzzled me a good deal ; still, in each case 



