120 



NATURE 



[Dec. 4, 1879 



chemists until Mr. Perltin successfully grappled with the subject 

 in 1856, and produced the beautiful colouring matter known as 

 aniline violet, or mauve, the production of which, on a large 

 scale, by Mr. Perkin, laid the foundation of the coal-tar colour 

 industry. 



His more recent researches on anthracene derivatives, especially 

 on artificial alizarine, the colouring matter identical with that 

 obtained from madder, rank among the most important work, 

 and some of them have greatly contributed to the successful 

 manufacture of alizarine in this country, whereby we have 

 been rendered independent of the importation of madder. 



Among the very numerous researches of purely scientific 

 interest which Mr. Perkin has published, a series on the hydrides 

 of salicyl and their derivatives, may be specially referred to ; 

 but among the most prominent of his admirable investigations 

 are those resulting in the synthesis of coumarin, the odoriferous 

 principle of the tonquin bean and the sweet scented woodruff, 

 and of its homologues. 



The artificial production of glycocol and of tartaric acid by 

 Mr. Perkin conjointly with Mr. Duppa, afford other admirable 

 examples of synthetical research, which excited very great 

 interest among chemists at the time of their publication. 



It is seldom that an investigator of organic chemistry has 

 extended his researches over so wide a range as is the case with 

 Mr. Perkin, and his work has always commanded the admiration 

 of chemists for its accuracy and completeness, and for the origin- 

 ality of its conception. 



A Royal Medal has been awarded to A. C. Ramsay, F.R.S. 

 Prof. Ramsay has been for a period of nearly forty years 

 connected with the Geological Survey of Great Britain, and 

 during by far the greater part of that time either as Director or 

 Director -General of the Survey. During this long period, in 

 addition to his official labours in advancing our knowledge of 

 the geology of this country, he has published works on the 

 " Geology of Arran, " "The Geology of North Wales," "The 

 Old Glaciers of North Wales and Switzerland," and "The 

 Physical Geology and Geography of Great Britain," now in its 

 fifth edition. ,His papers in the Quarterly Journal of the 

 Geological Society, and elsewhere, are numerous and important, 

 especially those on theoretical questions in physical geology, such 

 for instance, as "The Glacial Origin of Lake Basins, The 

 Freshwater Formation of the Older Red Rocks," and "The 

 History of the: Valley of the Rhine, and other Valleys of 

 Erosion." There are, indeed, among living geologists few who 

 can claim to have done more to extend our knowledge in the 

 important fields of geology and physical geography. 



The Davy Medal has been awarded to P. E. Lecoq de Boisbau- 

 dran. The discovery of the metal gdlium is remarkable for 

 having filled a gap which had been previously pointed out in the 

 series of known elements. Mendelejeff had already shown that 

 a metal might probably exist, intermediate in its properties 

 between aluminium aud indium, before Boisbaudran's laborious 

 spectroscopic and chemical investigation of numerous varieties 

 of blende led him to the discovery and isolation of such a metal, 



The separation of the minute traces of gallium compounds 

 from blende is an operation presenting unusual difficulty, owing 

 to the circumstance that compounds of gallium are carried down 

 by various precipitates from solutions which are incapable by 

 themselves of depositing those compounds. 



EXPERIMENTAL DETERMINATION OF THE 



VELOCITY OF LIGHT* 



II. 



"pIG. 7 represents a plan of the lower floor of the building. 1: 

 is a three horse power Lovegrove engine and boiler, resting 

 on a stone foundation ; B, a small Roots' blower ; G, an automatic 

 regulator. From this the air goes to a delivery pipe up through 

 the floor to the turbine. The engine made about four turns per 

 second, and the blower about fifteen. At this speed the pressure 

 of the air was about half a pound per square inch. 



The regulator, Fig. 8, consists ol a strong bellows, supporting 

 a weight of 370 pounds, partly counterpoised by 80 pounds, in 

 order to keep the bellows from sagging. When the pressure of 

 the air from the blower exceeds the weight, the bellows com- 

 mences to rise, and in so doing closes the valve, v. 



This arrangement was found in practice to be insufficient, 

 and the following addition was made : a valve was placed 



1 By Albert A. Michelson, Master, U.S. Navy. Read before the 

 American Association. Continued from p. 56, 



at r, and the pipe was tapped a little farther on, and a rub- 

 ber tube led to a water gauge, Fig. 9. The column of water in 

 the smaller tube is depressed, and when it reaches the horizontal 

 part of the tube, the slightest variation of pressure sends the 

 cilumn from one end to the other. This is checked by an 

 assistant at the valve, so that the column of water is kept at 

 nearly the same point, and the pressure thus rendered very nearly 

 constant. The result was satisfactory, though not in the degree 

 anticipated. It was possible to keep the mirror at a constant 

 speed for three or four seconds at a time, and this was sufficient 

 for an observation. Still it would have been more convenient to 

 have kept it so for a longer time. The test of uniformity was, 

 however, very sensitive, as a change of speed of 0*02 of a revo- 

 lution per second could be detected. 



Fig. 7. 



It was found that the only time during the day when the 

 atmosphere was sufficiently quiet to get a distinct image was 

 during the hour after sunrise or during the hour before sunset. 

 At other times the image was " boiling," so as not to be recog- 

 nisable. In one experiment the electric light was used at night, 

 but the image was no more distinct than at sunset, and the light 

 was unsteady. 



The method followed in experiment was as follows : — The fire 

 was started half an hour before, and by the time everything was 

 ready the gauge would show 40 or 50 lbs. of steam. The mirror 

 was adjusted by signals as before described. The heliostat was 

 placed and adjusted. The revolving mirror was adjusted by 

 being moved about till the light returned to it from the distant 

 mirror. The axis of the revolving mirror was also inclined to 



Fig. 8. Fig. 9. 



the right or the left, so that the direct reflection of light from 

 the slit fell above or below the eyepiece, as otherwise this light 

 would overpower that from the reflection from the distant mirror, 

 &c, which forms the image to be observed. This inclination of 

 the axis of rotation introduces a small error, which is duly 

 allowed for in the calculations. 



The distance between the front face of the mirror and the cross 

 hair of the eyepiece was then mea-ured, by stretching from one 

 to the other a steel tape, making the drop of the catenary about 

 an inch — when the error on account of the curve, and that due to 

 the stretching of the tape, ju-t counterbalanced each other. 



The position of the slit, if not determined before, was then 



