UNDULATORY FORCES. LIO HT PHOTOGRAPH Y. [WXCICDINO REMAKKS. 



We must, however, remark, that the art of pi 

 graphy, perhaps, of all others, is continually undergoing 

 rapid change and improvement; and if any of our 

 reader* have been 10 far interested in our experiment*, 

 *c., as to be induced to repeat thorn, wo may state, that 

 the various photographic periodicals may, at all times, 

 be advantageously consulted ; because, by thorn, tlio new 

 processes, as they are made public, may be learned, and 

 considerable saving of time and money effected. 



Despite the elaborate treatises which have been pub- 

 lished, the chemistry of photography is as yet but 

 imperfectly understood. The varying character of the 

 numerous recipes which we have given for solutions, 

 baths, *c., proves that, to a great extent, empiricism, 

 rather than strict scientific rule, is the order of the day. 

 Indeed, if our readers had the patience and time to 

 wade through the various processes which are contin- 

 ually being published, and would compare the directions 

 given with such processes, for instance, as those of the 

 electrotype, they would at once perceive the absence of 

 exactness and precision which should always bo sought 

 after in the application of experimental philosophy. 

 Many a discovery in the art has been made by an acci- 

 dental mixture of chemicals ; and frequently pure acci- 

 dent has been the best assistant to photographic pro- 

 gross. We may state, that photography stands now in a 

 somewhat similar position to what alchymy does to 

 chemistry ; and it is almost certain, that all our suc- 

 cesses hitherto will form but the introduction to others 

 of a far more enlarged kind. This, however, is a mat- 

 ter of great importance and of encouragement to every 

 attentive student, because an accident may just as 

 readily lead him to new and valuable discoveries as it 

 would the most practised hand. In mathematics a new 

 discovery is almost impossible, so well has that branch 

 of human knowledge been investigated ; but in experi- 

 mental science, we are continually stumbling over a 

 novelty which often only requires elaboration to convert 

 into a valuable addition to our stock of well-ascertained 

 facts. 



Addressing ourselves to our young readers, or to self- 

 taught students, we would observe, that however often 

 a process or experiment be repeated, something new 

 may be detected if close and keen observation be em- 

 ployed. There are hundreds of class experiments 

 that have been long well known to every scientific in- 

 quirer, which present new features on each repetition. 

 Indeed, many of our most important discoveries have 

 been made from occurrences which are familiar to every 

 human being. The invention and perfection of the 

 steam-engine, by James Watt, is a remarkable instance 

 of the kind. Applying these remarks to photography, 

 wo may state, that no two collodionised plates ever pre- 

 sent the same appearances ; the effect of developing 

 solutions equally varies ; and so on. Now, as each of 



these variations has ita own cause, and cannot be the 

 result of .;.-. i.l. nt as such must take plare a. cording to 

 some definite, although, perhaps, unknown law we 

 cannot but perceive that a failure always contains a 

 germ of some future success ; whilst success itself, like 

 prosperity in life, often hides that which would become 

 a great advantage. 



We make these remarks with another object : it is 

 that of urging on all, the duty of at once making public 

 any fact of importance which they may moot with. 

 This is easily done by communicating the particulars in a 

 terse, pithy manner to any of the photographic societ irs 

 or periodicals, each of which is at all times open to the 

 reception of useful information. The discovery of a 

 now principle or fact, does not constitute a right of 

 property in its discoverer, however justly he may make 

 its application a niAttcr of profit The laws of nature 

 are the property of every man; but as the application 

 of each requires special training and character of mind, 

 it is only just that those who have such acquirements 

 (and they are only to be obtained by great patience and 

 perseverance) should reap a proper reward for their 

 exercise. This spirit, we are happy to say, has been 

 eminently observed throughout the history of photo- 

 graphy, and is as creditable to its possessors as it has 

 proved beneficial to society at large. By pursuing tho 

 course we are recommending, the experimenter, whilst 

 assisting his co-workers, will put forward, by his genero- 

 sity, a claim on them for reciprocal conduct, and the 

 result will be a rapid advance in every branch of this 

 interesting art. 



Having thus investigated the laws of light, and 

 their applications, we shall now direct attention to 

 the phenomena presented by another of tho undulatory 

 forces namely, that of Electricity. We shall find many- 

 analogies between it and heat and light ; some of which 

 we have already pointed out in our general introduction 

 to physical science.* The subject on which wo are 

 about to enter, affords a vast variety of interesting and 

 brilliant experiments, and will so far relieve the mind 

 of the tyro by exciting simultaneously the eye and the 

 mind. The science of light is necessarily of consider- 

 able difficulty, although of deep interest : it involves 

 an intelligent and deep study, especially in connexion 

 with mathematical science, of which it is a most im- 

 portant application. For the sake of simplifying the 

 subject, we have avoided, as far as possible, all diffi- 

 culties of the kind, and have therefore given results 

 rather than extended details. 



Electricity, on the other hand, is a purely experi- 

 mental subject : many of its phenomena are familiar to 

 every one ; and we trust that our exposition of them 

 will suffice to give the attentive reader a general know- 

 ledge and insight into its laws and applications. 



Sec ante, p. 1, tt Hq. 



ADDENDA ON THE SPECTRUM ANALYSIS. 



AT the time our remarks on the new discoveries of Messrs. 

 I'.iinsen and Kirchkoff were written,t the publish"! 

 information on the subject was very imperfect. We 

 h:iv, therefore, availed ourselves of a most interesting 

 paper, read by Dr. Miller, at the meeting of tho British 

 Ansociation in Manchester, in September, 18G1; and are 

 indebted for a n'tumf and engnvings to the London 

 10, of Oct. 6th, in which a full report may be found. 

 The learned professor commenced by giving historical 

 details of the various discoveries which had been made 

 in connection with tho subject, from tho tim6 of Newton 

 to the present day; to which we have previously referred 

 incidentally. Many facts bearing on the question have 

 already been mentioned in the previous pages ; we shall, 

 therefore, confine our extracts to the practical details and 

 results obtained by recent experimenters on the Photo- 

 graphic Spectra of the Electric Light, in contrast with 

 those of the solar rays. 



I Sw ante, p. M. 



161 _ 



ON THE PHOTOGRAPHIC SPECTRA OF THE 



ELECTRIC LIGHT. 



"A plan of the apparatus by which the spectra maybe 

 photographed is shown in the figure (Fig. 101). It con- 

 sist* of an ordinary ca- 

 mera-obscura, C, attached 

 to the end of a long wooden 

 tube, A, which opens into 

 a long cylindrical box, B, 

 within which is a prism of 

 heavy flint glass, or of bi- 

 sulphide of carbon, i. At I 

 is a lens of 15 inches focal 

 length, and at s is a slit 

 parallel to the axis of tho 

 L Tho slit is ad- 

 justed BO that it shall bo Appnratn. for rhotoKraphin* tpMtn. 

 distant from the lens 30 inches or twice its focal length, 

 and tho screen of the camera is at an eqn;il <iist;im-e from 



