SCIENCE. 



293 



ous wings and were probably aquatic in early life. The 

 last statement is simply inferred trom the fact that all the 

 modern types most nearly allied to them are now aquatic. 



" Some of the Devonian Insects are plainly precursors of 

 existing forms, while others seem to have left no trace. 

 The best examples of the former are Platephemera, an 

 aberrant form of an existing family ; and Homothetus which, ! 

 while totally different in the combination of its characters i 

 from anything known amang living or fossil insects, is the 

 only Palaeozoic insect possessing that peculiar arrangement 

 of veins found at the base of the wings in Odonata typified 

 by the arculus, a structure previously known only as early 

 as the Jurassic. Examples of the latter are Gerephemera, 

 which has a multiplicity of simple parallel veins next the 

 costal margin of the wing, such as no ether insect ancient 

 or modern is known to possess ; and Xenoneura, were the 

 relationship of the internomedian branches to each other 

 and to the rest of the wing is altogether abnormal. 



" If, too, the concentric ridges, formerly interpreted by 

 me as possibly representing a stridulating organ, should 

 eventually be proved an actual part of the wing, we should 

 have here a structure which has never since been repeated 

 even in any modified form. 



'•They show a remarkable variety of structure, indicating 

 an abundance of insect life at that epoch. 



" The Devonian Insects also differ remarkably from all 

 other known types, ancient or modern ; and some of them 

 appear to be even more complicated than their nearest liv- 

 ing allies. 



"We appear, therefore, to be no nearer the beginning of 

 things in the Devonian epoch than in the Carboniferous, so 

 far as either greater unity or simplicity of structure is con- 

 cerned ; and these earlier forms cannot be used to any bet- 

 ter advantage than the Carboniferous types in support of 

 any special theory of the origin of insects. 



" Finally, while there are some forms which, to some de- 

 gree, bear out expectations based on the general derivative 

 hypothesis of structural development, there are quite as 

 many which are altogether unexpected, and cannot be ex- 

 plained by that theory without involving suppositions for 

 which no facts can at present be adduced." 



MICROSCOPY. 



Mr. W. H. Bullock, of Chicago, the maker of the micro- 

 scope for lithological work described by us in Vol.. I, No. 

 21 of Science, writes to us, objecting to an editorial remark, 

 that the arrangement of the polariscope for instant use, 

 claimed as a noveltv by Mr. Bullock, had been used in 

 the same position by Swift, of London, for many years. 



Mr. Bullock admits the accuracy of this statement, but 

 now sends details, as evidence, that he has shown consider- 

 able ingenuity in arranging his analyzing prism, "mounting 

 it in such a manner, that it can be turned round 90 degrees, 

 so that when the lower prism is at the spring stop or zero 

 point, and the upper prism is pushed into position with the 

 indicator forward, the prisms are parallel, and upon its be- 

 ing turned back or revolved 90 degrees the prisms are 

 crossed." ■' The lower prism is also arranged differently to 

 that used by Swift ; it can be fitted either to the sub-stage 

 or used in the supplementary sub-stage, and thus used close 

 under the stage, so that no light can reach the object under 

 observation, except that which passes through the lower 

 prism." Mr. Bullock also notices other improvements 

 which must render the instrument very perfect for the pur- 

 poses for which it was designed, namely, lithological work. 

 Mr. Bullock sends a photograph of this microscope and 

 we readily admit that it appears to be an excellent instru- 

 ment ; of the workmanship we are, of course, unable to 

 speak, but probably the reputation of Mr, Bullock is 

 sufficient guarantee in this respect. 



New York Academy of Sciences. — Section of 

 Chemistry. — Monday Evening, December 13, 1880, at 8 

 o'clock, the following paper, by Dr. Henry A. Mott, is 

 announced :— Chemical Decomposition incited by a Cold 

 Fluid Stratum floating on a Warm Liquid, 



ASTRONOMY. 

 JUPITER. 



MOTION OF SPOTS ON HIS SURFACE. 



Jupiter, always enigmatical, has, since the appearance 

 of the great ied spot in his Southern hemisphere, become 

 more and more perplexing. It was supposed this object 

 would afford a ready means of determining Jupiter's true 

 period of rotation. It has not done this, but has certainly 

 led to the development of many interesting facts, one of 

 which is that no period can be determined, because there 

 are not two parts of the planet's visible surface which 

 rotate in equal times. It would seem reasonable that any 

 two poipts on the same parallel of latitude and in the 

 same hemisphere must necessarily rotate with equal 

 velocities ; this does not even hold good. Could we be 

 placed in such a position that the rotation of the planet 

 would not visibly change the position of objects on his 

 surface, we should still see the spots moving not only 

 with different velocities, but in contrary directions. Spots 

 very rarely change their latitude, as the very great axial 

 rotation of Jupiter confines their motion to a parallel 

 with his equator. In Jupiter's Southern hemisphere are 

 two or three small dusky cblong spots. The most dis- 

 tinct of these I first observed on the morning of July 25, 

 1880, (see English Mechanic, No, 804, where an engrav- 

 ing showing its position is given). This group of small 

 spots lies on a parallel of latitude about even with the 

 Southern edge of the great red spot. On July 25, the 

 centre of the first observed of the spots preceded the 

 centre of the large spot by ih. 35m. Since that date the 

 red spot has been observed constantly, and the small one 

 frequently. Up to November 23, thirty-five transits of 

 the great spot across the central meridian, and nine of 

 the smaller have been carefully observed. On November 

 22, the small spot preceded the greater by 3*1. 17m. 

 The interval between their transits having increased ih. 

 42m. since July 25. The large spot has moved backward, 

 compared with the direction of rotation, making its 

 transit on November 22 occur 49m. later than on July 25, 

 while the small spot came to its transit 53m. earlier 

 than on July 25, showing that the two are moving with 

 nearly the same velocity, but in opposite directions. The 

 mean daily drift backward of the great spot since July 

 25 has been 0.40245m, while the forward motion of the 

 small spot has been, during the same period, 0.43948m 

 per day. It will be seen from this that a rotation derived 

 from the small spot would indicate a quicker period than 

 that derived from the large red spot. 



From the observations of July 25 and Nov. 22, the 

 great spot rotates in 9!). 55m. 37.065s., and the small 

 one in 9h. 55 m. 16. 176s. The mean rotation of the two 

 is 9I1. 55m. 26.621s. A reduction of all the observa- 

 tions on hand will, doubtless, slightly change these figures. 

 It would be well for observers to watch this small spot, 

 as it may last as long as the large one. If it should con- 

 tinue permanent, it will eventually make the circuit of 

 Jupiter and meet the red spot ; this would occur about 

 the middle of February, 1882. 



But the motion of these two objects is very slow com- 

 pared with the rapidly moving black spots which appeared 

 just north of the equatorial belt on the last of October. 

 But as attention has already bten called to these remark- 

 able objects by Messrs. Dennett, Williams and Denning, 

 in English Mechanic, No. 816, I will not refer to them 

 here, further than to say that they have been observed 

 and sketched as often as the weather wculd permit since 

 their first appearance. The region occupied by the great 

 equatorial belt is subject to constant and quite rapid 

 change, being filled at times with the most delicately soft 

 plumey forms. Brilliant white spots are not unfrequent 

 in this zone. These bright spots generally appear as in- 

 tensely white heads, followed by a light, diffused and 

 fainter train. Sometimes this train is composed of light, 



