622 



KNOWLEDGE ♦ 



[May 26, 1882, 



An oxpondituro of much patience may be necessary 

 before satisfactory negatives of tlio moon will bo obtained, 

 but as soon as the actiivc focus lias been found approxi- 

 mately, the work on each evening will be more easy ; but 

 one or two trials must bo made to test the focus, which 

 will vary with tho temperature, owing to the alteration of 

 the length of tho telescoj)e tube. 



In ordf^r to show the eUVct of atniospheric disturbance, 

 a photograph of any bright star may be made — Sirius, for 

 instance. Put tlie plate in position, and then, the tele- 

 scope being at rest, allow the image of the star to pass 

 across the sensitive film ; on development, it will be found 

 that, instead of a straight line, it will be of zig-zag form. 

 This atmospheric disturbance, of course, aflects the picture 

 of the moon, and it is not easy to distinguish between this 

 defect and the incorrect focus. It may be necessary to 

 take dozens of negatives in order to secure one good one. 

 For this reason, tliere is a great saving of time if the plate 

 be arranged so that four pictui-es can be taken successively, 

 the times of exposure being varied. 



In a future paper, the gelatine dry plate process will be 

 described. This process is very much more rapid than wet 

 collodion, and it may be thought that, for that reason, it 

 should be preferred for astronomical photography ; but up to 

 the ])resent time the best photographs of the moon have 

 been taken by the wet process, and so far as my own ex- 

 perience extends, the dry gelatine plate is not so suitable 

 for enlarging — much of the finer detail of the original nega- 

 tive is lost in enlarging by either process, and there can be 

 no doubt that the long-neglected Daguerreotype plate 

 would give better re.sults than any of the more modern 

 processes. 



It will be necessary to examine each negative with a 

 lens, in order to judge whether sufficient sharpness of detail 

 has been obtained, selecting the craters near the terminator 

 of the moon as tests. 



One of the most curious and interesting results of the 

 application of photography to astronomical observation is 

 in the combination of two pictures of the full moon to be 

 viewed in the stereoscope. By selecting negatives that 

 have been taken in suitable states of the libration of the 

 moon, and by mounting transparencies (in preference to 

 paper), enlarged to the same size, we obtain a picture 

 showing the rotundity of the moon in a very remarkable 

 way. 



T>ie diameter of the images of the planets in telescopes 

 of moderate size is so small, that no results of any value 

 can be obtained. 



The great value of photography, as applied astro- 

 nomically, has been in determining, first, that the red 

 flames seen during total eclipses of the sun really belonged 

 to the sun ; and, more recently, the much-disputed question 

 as to the solar corona was finally disposed of by comparing 

 photographs taken at stations widely separated. 



PROF. HUXLEY ON SCIENCE AND CULTURE.* 



LIKE others of the most valuable works by Prof. 

 Huxley, the book before us is a contribution rather 

 to literature than to science, though tho author derives 

 some of liis most efTcotive arguments and illustrations from 

 science. The Essays, Lectures, and Addresses which form 

 the volume are gathered from various magazines in which 



•"Soienoo and Culture, and other Essays." By T. H. Huxlev 

 LL.D., P.B.S. (Messrs. Macmillan & Co., Loudon.) 



they have appeared at intervals during seven or eight past 

 years. Home critics (mostly those who, being themselves 

 essayists, can find none to publish^volumes of their collected 

 papers) take strong exception to the course thus pur- 

 sued by Prof. Huxley. Such a critic, in reviewing 

 a volume of essays by the present writer, said that to 

 collect and republish essays which have already appeared 

 was the worst possible oflTonce ; and another compared 

 the author of such a volume to a liighwayman holding a 

 pistol in the form of an octavo volume at the head of an 

 unoffending public. The answer is obvious. If the 

 public does not like such works, the public can and does 

 leave them alone ; V)ut if the public finds an author's re- 

 published essays worth re-reading, the author is some- 

 thing more than justified in republishing them. It appears 

 — who, indeed, could douVjt it 1 — that Professor Huxley's 

 readers are of this opinion. " I can give no better reason 

 for republishing [these papers] in their present fonn," he 

 says, " than tho fact that three earlier collections of a 

 similar form have been received with favour." .i\jad a very 

 sound and sufficient reason it is. 



The first paper — an address on science and culture — is 

 interesting for the strong, yet moderate, assertion of Pro£ 

 Huxley's claim for pure science as a necessary part of 

 culture. He rejects, on the one hand, the arguments of 

 self-styled practical men (expressing in passing a belief, in 

 which we wish we could share, that " the pure species has 

 been extirpated "), and, on the other, those of certain clas- 

 sical scholars, who consider themselves, as it were, Levites 

 in charge of the ark of culture. He shows very clearly 

 the distinction between the mere Latinism of the Middle 

 Ages and the true classical culture'of the Renascence. He 

 pokes a very clever joke at the advocates of merely scho- 

 lastic training, where he says that " if we were disposed 

 to be cruel, we might iirge that they have brought re- 

 proach upon themselves, not because they are too full of 

 the spirit of the ancients, but because they lack it." 

 " Modern astronomy," he says justly, " is the natural con- 

 tinuation and development of the work of Hipparchus and 

 of Ptolemy ; modern physics of that of Democritus and of 

 Archimedes ; it was long before modern biological science 

 outgrew the knowledge bequeathed to us by Aristotle, by 

 Theophrastus, and by Galen." " We cannot know all the 

 best thoughts and sayings of the Greeks unless we know 

 what they said about natural phenomena. We falsely 

 pretend to be the inheritors of their culture, unless we are 

 penetrated, as' the best minds among them were, with an 

 unhesitating faith that the free employment of reason, in 

 accordance with scientific method, is the sole metliod of 

 reaching truth." This lesson from the ancients is, indeed, 

 the key note of the first six of the Addresses, Lectures, 

 and Essays gathered together in the present voluma 

 Scattered through those essays there are numbers of pithy 

 sayings, well worth quoting and remembering. Here area 

 few of them : — " An exclusively scientific training will bring 

 about a mental twist, as surely as an exclusively literary 

 training." " Knowledge is only the servitor of wisdom " 

 (may this, our Knowledoe, be so regarded !) " Do what 

 you can to do what you ought, and leave hoping and fear- 

 ing alone." "The assertion which outstrips evidence is 

 not only a blunder but a crime." "The Nemesis of all 

 reformers is finality." "When you cannot prove that 

 people are wrong, but only that they are absurd, the best 

 course is to let them alona" (Note that, Mr. Editor of 

 Knowledge !) 



The other essays are more specially scientific. In 

 them Professor Huxley deals with the Border Terri- 

 tory between the Animal and Vegetable Kingdoms. 

 Certain Errors respecting the Structure of the Heart, 



N 



