272 THE POPULAR SCIENCE MONTHLY. 



and devoting all his energies to his chosen science in a city which was 

 then the most famous in the world for its astronomical instruments ; 

 and the other, a mere hoy, oppressed hy narrow circumstances, work- 

 ing in the intervals of his college duties with a telescope which he had 

 himself constructed, with a fellow-student (Mr. Hamilton L. Smith) as 

 his only assistant. 



The work of both astronomers (for it is impossible to deny to Mason 

 that title) is of great excellence, but it will not be claiming too much 

 to assert that Mason's was by far the most valuable monographic study 

 of a nebula which had appeared, and indeed, in its thorough appre- 

 ciation of the problems to be solved and in its most skillful adapta- 

 tion of the existing means toward that end, it deserves to rank with 

 the greatest works of this class, with Bond's, Lassell's, liosse's and 

 Struve's. It is not only in the observations themselves nor in the ex- 

 quisite and accurate drawings which accompany tlie memoir that we 

 feel this excellence, but in the philosophical grasp of the whole sub- 

 ject and the masterly appreciation of the fundamental ideas of the 

 problem. His memoir contains so much that bears on this general 

 aspect, that we quote from it largely, as it is too little known among 

 those not professional astronomers : 



" Although a period of nearly fifty years has now elapsed since the researches 

 of the elder Herschel exposed to us the wide distribution of nebulous matter 

 through the universe, we are still almost as ignorant as ever of its nature and 

 intention. The same lapse of time that, among his extensive lists of double 

 stars, has revealed to us the revolution of sun around sun, and given us a partial 

 insight into the internal economy of those remote sidereal systems, has been ap- 

 parently insufficient to discover any changes of a definite character in the nebula), 

 and thereby to inform us at all of their past history, the form of their original 

 creation, or their future destiny. At the same time, the detection of such 

 changes is '\\\ the highest degree desirable, since no other sources of evidence 

 can be safejy relied upon in these inquiries. That the efforts of astronomers 

 have thus far ended, at least, in vague and contradictory conjectures, is princi- 

 pally attributable to the great difficulty of originally observing, and of describing 

 to future observers, bodies so shapeless and indeterminate in their forms, with 

 tlie requisite precision. For we cannot doubt, authorized as we are to extend 

 the laws of gravitation far into the recesses of space, that tliese masses of dif- 

 fused matter are actually undergoing vast revolutions in form and constitution. 

 The main object of this paper is to inquire how far that minute accuracy which 

 has achieved such signal discoveries in the allied department of the double stars 

 may be introduced into the observation of nebuhiB, by modes of examination and 

 descrip/tion more peculiarly adapted to this end tlian such as can be employed 

 in general reviews of the heavens. ... It will conduce to a clearer under- 

 standing of our object to point out, generally and rapidly, the distinctions be- 

 tween our own theory of observation and that commonly adopted. It consists 

 not in an extensive review, but in confining the attention to a few individuals; 

 upon these exercising a long and minute scrutiny, during a succession of evenings; 

 rendering even the slightest particulars of each nebula as precise as repeated ob- 

 servation and comparison with varied precautions can make them, and confirm- 

 ing each more doubtful and less legible of its features by a repetition of suspi- 



