402 SCIENTIFIC RECORD FOR 1885. 



Rowland^ s photograph of the normal solar spectrum. — This map has been 

 made by Professor Eowland of the Johns Hopkins University, with one 

 of his concave gratings of 21^ feet radius of curvature and 6 inches di- 

 ameter, and is now complete from wave-length 3680 to 5790 ; the portion 

 above 3680 to the extremity of the ultra-violet, wave-length about 3100, 

 is nearly ready. Negatives have also been prepared down to and includ- 

 ign B, and it is possible they may be prepared for publication ; a scale of 

 wave-lengths has been added. " The error in the wave-length at no 

 part exceeds gowo of the whole, and is generally caused by a slight 

 displacement of the scale, which is easily corrected. The wave-lengths 

 of more than 200 lines in the spectrum have been accurately determined 

 to about 5ooWd P^^t, and these can serve as standards to correct any 

 small error of the scale. - - - The 1474 line is widely double, as 

 also 63 and 64, while U is given so nearly double as to be recognized as 

 such by all persons familiar with sj)ectrum observation. Above the 

 green the superiority increases very quickly, so that at S we have 120 

 lines between H and K, while the original negatives show 150 lines. 

 The photographs show more at this point than the excellent map of 

 Lockyer of this region." 



THE PLANETS. 



Intra-mercurial planet. — The report* of a committee of the Na- 

 tional Academy of Sciences, to which was referred the question of the 

 expediency of fitting out an expedition to the west coast of Africa for 

 the purpose of observing the total eclipse of the sun on August 28-29, 

 1886, contains the following remarks in regard to the hypothetical planet 

 revolving within the orbit of Mercury : " In addition to the observation 

 of the sun itself, and the luminous phenomena attending it, it is desir- 

 able to obtain photographic maps of all the surrounding region to the 

 distance of at least ten or fifteen degrees from the sun, for the purpose 

 of finally setting at rest the still mooted question of an intra-mercurial 

 planet. It is true that the astronomical world is at present disposed 

 generally to discredit the existence of such a body, yet the evidence on 

 the subject up to this time is mainly negative, as it must always con- 

 tinue to be so long as it depends upon direct vision. In a photographic 

 map, taken during total eclipse of the sun, of the whole region within 

 which such a planet must necessarily be confined, the object, if present, 

 must present itself, and could not fail to be recognized. But for photo- 

 graphic operations of this class, lenses of wide angle must be specially 

 prepared, differing essentially in character from those which are em- 

 ployed to take impressions of the eclipse." 



A search for the " supposititious Vulcan" was again made by Mr. T. 

 W. Backhouse, of Sunderland, England, in March and April, 1885— the 

 period during which a transit is possible, according to Leverrier — but 



* Senate Ex. Doc. No. 67, Forty-ninth Congress, first session. 



