94 



SCIENCE. 



the use of immersion objectives, which are now in 

 universal use, and accepted as a valuable improvement. 



The use of oil was suggested by Amici, as far back as 

 1844, by Oberhauser in 1845, ar >d Wenham in 1855 and 

 again in 1870, and only admitted in practice in 1878, so 

 that it appears to have required 34 years to convince 

 microscopists of a fact, that might have been settled in a 

 week and this due to " persistence in a fallacy." Such 

 being the case it is surely time for these fallacies to be 

 shelved, and we are glad to find the R. M. S. has taken 

 such a view of the case. 



FLUORESCENT BODIES. 



If we put some common paraffin oil, or a solution of 

 sulphate of quinine, into a glass tube or other suitable 

 vessel, and then look through it, the liquid will appear 

 quite colorless ; but if we allow the light to fall upon it, 

 and then view it at a little distance and at a certain 

 angle, some parts of the liquid will present a delicate sky- 

 blue tinge. The effect in the case of quinine is height- 

 ened if the source of light is burning magnesium wire. 



The large number of substances belonging to this class 

 are termed fluorescent bodies, because they exhibit pheno- 

 mena similar to the examples above given. The term 

 itself, however, was suggested to Prof. Stokes by a par- 

 ticular kind of fluor-spar which shows this property. 



Again, if we cause a room to be darkened, and allow 

 only blue light (/. e., by covering a hole in a window- 

 shutter with cobalt-blue glass) to fall upon a glass vessel 

 filled with water which has been standing some minutes, 

 on floating a strip of horse-chestnut bark upon its surface, 

 in a few moments a stream of bluish grey fluid (sesculin) 

 will be seen slowly descending from the bark, hanging, in 

 fact, like a bunch of barnacles from an old ocean waif. 

 Of if, under the same arrangement of light, or by using 

 even more powerful absorbents of the ordinary rays (such 

 as a solution of ammonio-sulphate of copper or one of 

 chromate of potash), we look at a piece of what is com- 

 monly termed canary glass — t. e., glass colored with an 

 oxide of the metal uranium — it will be seen to glow as it 

 were with rich greenish yellow rays, just as though it were 

 itself a source of light ; or if we take a solution of a 

 uranium salt (the normal acetate) the phenomena are very 

 striking when examined under the same conditions, and 

 still more so by the electric light. But the salts of ani- 

 line — a substance which is the parent, so to speak of 

 mauve, magenta, and other brilliant colors — are singu- 

 larly rich in exhibiting these effects. 



A very beautiful experiment may be performed with 

 the aniline red ink now so commonly in use. It affords, 

 at one and the same time, an admirable illustration of 

 Prof. Tomlinson's submersion figures and of the phe- 

 nomena under consideration. If we take a long cylin- 

 drical glass vessel, or one with parallel sides, fill it with 

 water, which is allowed to settle, and then gently deliver 

 a drop of the red fluid to the surface, the drop begins to 

 contract, and slowly from its centre descends in the form 

 of a tube ; the denser parts of the coloring-matter pres- 

 ently form a thick circular rim at the end of the tube, — 

 but this is only for a moment, for a wavy edge appears 

 upon this rim, then expands into a triangular parachute 

 with a thickened edge, and from the extremity of each 

 corner two or three smaller tubes descend ; these in like 

 manner pass through the same phases as the parent 

 stem or tube.-is. R. Hodges ( Journal of Science, London.) 



INTRA-MERCURIAL PLANETS. 



A collection of the observations published in the report 

 of the Total Solar Eclipse of 1878, will give, perhaps, the 

 best idea of the present state of the question of the dis- 

 covery of Vulcan and other planets revolving within the 



orbit of Mercury ; and it may be of some interest to pre- 

 sent the matter in the form of a chart showing the 

 ground covered by different observers, who, during the 

 time of totality, devoted themselves to the search for 

 such bodies. For this purpose, the space swept by the 

 six observers, Newcomb, Hall, Wheeler, Bowman, Todd 

 and Pritchett, has been indicated by different shading on 

 the accompanying chart, which is merely a copy of that 

 prepared by Prof. Hall for the use of observers of the 

 eclipse, and published with the instructions issued from 

 the United States Naval Observatory. 



The two objects, " a " and " b," discovered by Prof. 

 Watson, and thought by him to be planets, have been 

 indicated upon the map thus : Q. The two discovered 

 by Swift, also announced as intra-mercurial planets, have 

 been marked thus : (g). 



Swift's two s f ars are described as equal in brightness, 

 of about the fifth magnitude, and 8' apart; on aline 

 with the sun's centre. Each had a round red disk, and 

 each was free from twinkling. The object farther from 

 the sun was at one time thought by Swift to be 1? Cancri, 

 and the other a new planet. The diameter of the field 

 of view was i.°5. 



Watson's star, " a," is described as being "between 

 the sun and # Cancri, and a little to the south ; " of a 

 ruddy color and about 4th magnitude, or fully a magni- 

 tude brighter than # Cancri, which was seen at the same 

 time. The star, " b," was also of a ruddy hue, and is 

 given as the 3rd magnitude. 



Wa'son used an aperture of 4 inches ; magnifying 

 power of 45 diameters ; Swift, an aperture of 4.5 inches ; 

 power of 25 diameters. We see by inspecting the chart, 

 that the place of one of Watson's stars ('that of which he 

 was the more certain) was covered by Wheeler with a 5- 

 inch aperture ; power 100 ; by Pritchett, 3.5 inch aperture, 

 power 90; and by Bowman with a 3.5 inch aperture and 

 power of 30 diameters. The place of Swift's two stars 

 was examined by Bowman and Wheeler, and one of the 

 stars appears just in the corner of Pritchett's sweep. 

 Finally, the whole ground was covered by Todd with a 

 4-inch aperture and power of 20. 



Ot these observers, Wheeler and Pritchett possessed tel- 

 escopes with optical power at least equal to that of Swift, 

 or Watson, and Bowman's glass was of sufficient power 

 to show any object as large as the 5th magnitude, — but 

 nothing, not already upon the chart, was found. 



This should be borne in mind, however, that several ot 

 the observers were enabled to make but very hasty 

 sweeps, — not devoting so much of their attention to the 

 subject as Watson did, and, indeed, at Mr. Todd's 

 station clouds interfered seriously with the work. And, 

 on the other hand, it appears that Prof. Watson devoted 

 a large part of his time to sweeping on the east side of the 

 sun. 



A glance at the chart will show that Watson's stars 

 have about the same relative positions and magnitudes 

 as ^ and C Cancri, and that Swift's stars as far as relative 

 position is concerned, resemble closely d 5 Cancri and 

 B. A. C. 2810, or the pair of stars similarly placed on the 

 other side of the sun. The probability of an error in 

 pointing the telescope, which would account for such a 

 misidentification as has been suggested, has been thor- 

 oughly discussed by Dr. C. H. F. Peters in the Astron. 

 Nach., No. 2253, p. 323, and Dr. Peters' paper has been 

 answered by Prof. Watson in the next volume, Astron. 

 Nach., No. 2263, p. 101. 



It is not the intention of this article to consider again the 

 question of the identity of the stars seen by Watson and 

 Swift, but merely to point out the evidence upon which 

 the discovery of " Vulcan " rests, and to call attention to 

 the fact that the existence of an intra-mercurial planet 

 is not yet admitted by the majority of astronomers of the 

 present day. W. C. W, 



Washington, D. C, February 24, 1881. 



