94 president's address — section a. 



show their satellites, and to record the places of the satellite of 

 Neptune, which it is difficult to see with any telescope, but is photo- 

 graplied easily ; to proving that the liji;ht round Venus in transit is 

 much brighter than the sunlight itself ; to recording the lines in 

 the ultra violet of the spectra of heavenly bodies, lines the exis- 

 tence of which otherwise must have lemained for ever unknown 

 to us, because they are invisible. 



We have taken only a passing glance at many of the applications 

 of photography, and each of them would repay a careful study. 

 Indeed, the results obtained by means of photograj^hy come upon 

 us so fast that one hardly realises their importance. Think for a 

 moment what it means to catch a fleeting ray of light that maybe 

 has for hundreds of years been flying through space with the 

 inconceivable velocity of 180,000 miles per second, to catch and 

 fix it on a ])hotographic plate, and extort from it, not only where 

 it came from, but the physical and chemical condition of the 

 star it came from — whether it be old or young, coming to us 

 or going away, whether the parent star has a bright or dark 

 companion, their dimensions, distance apart, speed in their orbits, 

 and their mass. To extort all this from a wandering ray of light 

 is more wonderful than anything in romance ; or, to turn in another 

 direction, the pliotographic survey of the heavens now in progress, 

 and many plates of which have been taken, will contain a record 

 of at least 3,500 stars for every 1 we can see with the eye. 



But grand as the work has been so far, there is yet much to do, 

 and more fields to conquer. It must replace the transit instrument 

 with another more accurate and capable of recording all stars to 

 the tenth or twelfth magnitude. It must find an instrument large 

 enough to record the closest double stars, and such clusters as 

 Omega Centauri. It must write at short intervals the exact forms 

 of nebulae as well as their spectra, showing motion in space, and so 

 record their changes in form as well as their disappearance and 

 appearance that any change will be detected ; must make still more 

 accurate records of the magnitudes and spectra of the stars ; must 

 sound the star depths in all directions so that photographs of star 

 clusters will show the stars still more accuiately, and must find an 

 automatic camera suited to its needs that will keep records of sun, 

 moon, and stars ; must picture the moon as perfectly as we can 

 see it, and make it possible to compare minute details month after 

 month, and so detect any changes. No doubt there are difficulties 

 in the way, and even this moderate view of the wants of the 

 future presents many, but they are not insuperable. The army of 

 science is in one respect like the army of war — it is stirred to 

 conquering effort by the difficulties that stand in the way. Given 

 a citadel to be won, and there is always a forlorn hope to Avin it. 

 Given a glimpse of one of nature's secrets — the photosphere, the 

 prominences, and the corona hidden by the sunlight, except for a 

 moment in each century — and at once you see the army : Huggins, 



