716 Scientifie Proceedings, Royal Dublin Society. 
The spectrometer, mounted in the manner here described, has: 
now been in use for more than a year, and has been thoroughly 
tested. It has been found most convenient both for making eye- 
piece observations, and for taking photographs; it has also been 
found completely light-tight. In proof of this last statement, we- 
may mention that we have exposed rapid photographie plates in 
the camera of the instrument for upwards of six hours, on bright 
sun-lit days, during the course of an investigation we have been, 
and are at present, making, in conjunction with Professor Hartley, 
F. R.S., upon the ultra-spark spectra of the elements, and have 
experienced no difficulty whatever from‘ fogging.” 
