826 THE POPULAR SCIENCE MONTHLY. 



resulting habit of mind is apt to influence conduct in other spheres, 

 where muscular power and nerve are of no avail is apt to cause 

 the daring of dangers which are not to be met by strength of limb 

 or by skill. Nature, as externally presented in precipices, ice- 

 slopes, and crevasses, may be dared by one adequately endowed ; 

 but Nature, as internally presented in the form of physical con- 

 stitution, may not be thus dared with impunity. Prompted by 

 high motives, Tyndall tended too much to disregard the protests 

 of his body. Over-application in Germany caused at one time 

 absolute sleeplessness for, I think he told me, more than a week ; 

 and this, with kindred transgressions, brought on that insomnia 

 by which his after-life was troubled, and by which his powers of 

 work were diminished ; for, as I have heard him say, a sound 

 night's sleep was followed by marked exaltation of faculty. And 

 then, in later life, came the daring which, by its results, brought 

 his active career to a close. He conscientiously desired to fulfill 

 an engagement to lecture at the Royal Institution, and was not to 

 be deterred by fear of consequences. He gave the lecture, not- 

 withstanding the protest which for days before his system had 

 been making. The result was a serious illness, threatening, as he 

 thought at one time, a fatal result ; and, notwithstanding a year's 

 furlough for the recovery of health, he was eventually obliged to 

 resign his position. But for this defiance of Nature there might 

 have been many more years of scientific exploration, pleasurable 

 to himself and beneficial to others ; and he might have escaped 

 that invalid life which for a long time past he had to bear. 



In his case, however, the penalties of invalid life had great 

 mitigations mitigations such as fall to the lot of but few. It is 

 conceivable that the physical discomforts and mental weariness 

 which ill-health brings may be almost compensated, if not even 

 quite compensated, by the pleasurable emotions caused by unflag- 

 ging attentions and sympathetic companionship. If this ever 

 happens, it happened in his case. All who have known the house- 

 hold during these years of nursing are aware of the unmeasured 

 kindness he has received without ceasing. I happen to have had 

 special evidence of this devotion on the one side and gratitude on 

 the other, which I do not think I am called upon to keep to my- 

 self, but rather to do the contrary. In a letter I received from 

 him some half-dozen years ago, referring, among other things, to 

 Mrs. Tyndall's self-sacrificing care of him, he wrote : " She has 

 raised my ideal of the possibilities of human nature." 



