n8 HERSCHEL AND HIS WORK 



duty was, under cover of a roof, to watch the clock, 

 and to enter the measurements or remarks of the 

 observer, as well as with the workman in attendance. 

 A " speaking-pipe," as it was then called, of variable 

 length to suit changes in his position, but 115 feet long 

 at the most, was devised and fitted up. Usually his 

 sister Caroline was the recorder who did the work, all- 

 night work at times. 



The mechanical skill shown in the construction of 

 the telescope was proved sixty years after by Herschel's 

 distinguished son, Sir John, in a letter already re- 

 ferred to, dated March 13, 1847 : " The woodwork of 

 the telescope being so far decayed as to be dangerous, 

 in the year 1839, 1 pulled it down (the operation com- 

 menced on December 5), and having cleared away the 

 framework, etc., piers were erected on which the tube 

 was placed, that being of iron, and so well preserved, 

 that although not more than one-twentieth of an inch 

 thick, when in the horizontal position it sustained 

 within it all my family, and continues to sustain 

 enclosed within it to this day, not only the heavier of 

 the two reflectors, but also all the more important 

 portions of the machinery, such as being of iron and 

 brass stood in no fear of decay, as well as all such 

 portions of the polishing apparatus as would go into it, 

 to the amount, I presume, of a great many tons, which 

 had, when I last saw it, produced no sign of weakness 

 or sagging down. This great strength and resistance 

 to decay is to be attributed to the peculiar prin- 

 ciple of its internal structure, which is, in effect, very 

 similar to that for which, in later times, a patent 

 has been taken out under the name of Corrugated 

 Iron Roofing, etc., but of which the idea was, I 



