( 509 ) 



This, however, has not been the case. 



The day of the eclipse. Through tlie unfortunate concurrence of 

 three entirely different disturbances, where two of them would not 

 have been able to prevent success, the results of the two slit-spectro- 

 graphs have come to nothing. 



The first of these disturbances happened as follows. Some hours 

 before the beginning of the eclipse, the steel band which transfers 

 the motion of the siderostat axis to the coelostat axis was broken 

 entirel}^ without my fault through a movement which was altogether 

 inadmissible for my part of the siderostat, which we used in common. 

 At one end of this band, which was . fixed between two copper plates 

 by means of two steel screws, the two holes through which these 

 screws passed were torn up. This effect could not possibly have 

 been reached by a stress of 100 kilograms. The fact that this happened 

 instead of the steel band simply sliding over the steel axis was the 

 best refutation of the often quoted opinion that this way to transfer 

 motion should not be reliable. The dust, inevitable in an eclipse 

 camp, naturally heightened the friction of the band on the axis. 

 Hence it is evident that the disturbance to be mentioned next would 

 have had no effect on the instrument if it had been in the condition 

 as it was before the fracture. Fortunately I had spare bands taken 

 with me and a new one could be put on, which operation, however, 

 cost three quarters of an hour of our time which began to grow 

 more and more precious, nor did this incident contribute to the 

 quietness so indispensable at an eclipse. 



During the first part of the first partial phase, as often as the 

 sun was visible through the clouds, we could control whether the 

 image of the sun fell on the slit and it could be easily kept there. 



Now, however, something happened which in America and in the 

 East Indies would have been utterlj^ impossible, but proved to be 

 inevitable in Spain as experience had taught me during a fortnight. 

 During the second half of the first partial phase, a little more than 

 a quarter of an hour before the critical moment mj assistant admitted 

 several persons near my apparatus. Against this I was altogether 

 powerless. It seems that one of these unwished for visitors has pushed 

 against the coelostat mirror and thus disturbed it, from which may 

 be inferred that the newly fastened band has more or less given way 

 at its fastening points and the friction on the axis was not sufficient 

 to prevent disturbance. 



Had not over and above — the third disturbance — the sky been 

 clouded and the sun for the rest of the time been invisible, I should 



