August 25, 1 881] 



NATURE 



389 



were of remarkable size, quite colossal in comparison with 

 shallow water or littoral forms. Of the three species of Colos- 

 sendei*, two of which are described as new, the smallest has a 

 span of 14 cm. between the tips of its outstretched leg*, while 

 the largest has an extent four times as great. A new genus 

 (Scaeorhynchus) has been established for a species with a span of 

 19 cm., a gigantic size as compared with the dimensions of its 

 nearest allies. The most abundant species of Nymphon is the 

 largest of that extensive genu=, and one species of a new genus 

 (Pallenopsis) is more than twice as large as any of the species of 

 allied genera, such as Fallene, which are known only from the 

 littoral zone. It is further interesting to note that in a number 

 of forms the visual organs (ocelli) are either rudimentary and 

 destitute of pigment, or are entirely absent. In Pallenopsis, 

 however, the ocelli are relatively of unusually great size. The 

 species of Scajorhynchus and Colossendeis show clearly from 

 anatomical evidence the complete independence of the accessory 

 legs and the firi^t yaXr of ambulatory legs, as had Ijeen already 

 proved by Dohrn from embryological data. In all cases the 

 palpi and accessory legs are supplied with nerves from the same 

 ganglion,, and this latter shows in the adult no indication of 

 being composed of two coalesced ganglia. But Dohrn states 

 that there are in the larvie of Achelia two ganglia. This ques- 

 tion is of great interest, having a direct bearing on the affinities 

 of these Pycnogons with the Arachnids. Mr. Wilson describes 

 ten species, of which one half are given as new, and with 

 figures. 



New Zealand Desmids. — As a contribution to our know- 

 ledge of the pretty green unicellular alga; known as Desmids, 

 which are to 1 e met with in New Zealand, Mr. Maskell's paper 

 in the recently-published volume of the Transactions of the New 

 Zealand Institute is most welcome. It would seem to render 

 more than probable the idea that these minute alga; are to a large 

 extent cosmopolitan. The author is evidently under great dis- 

 advantage as to identifying the species he meets with, but this is 

 to a great extent done away with by his fairly careful descrip- 

 tions and accurate (as to outline) figures. He enumerates 

 between sixty and sixty-five species, some of which are very 

 noteworthy and fine additions to the list of Desmids ; thus 

 Apto^omim undidattim is a highly interesting new species. 

 Triplocaas bidentatum is not only a very distinct, but also a very 

 noble, new species, and equally distinct as a species is his Clos- 

 terium selencriim. Doubtless a more prolonged search in fresh 

 localities will enable the author to add many old and new spe- 

 cies to the list. He may feel sure that his further researches will 

 be looked for with interest by those working at the freshwater 

 alga; in Europe. 



Protoplasm "Stained whilst Living. — Mr. L. F. Henne- 

 guy publishes the result of some experiments made on living 

 infusoria, in which he confirms the observations of Brandt, made 

 in 1S79, that an aqueous solution of aniline brown, known in 

 commerce as Bismarck brown, will give an intense brownish- 

 yellow colour to the protoplasm of the infusoria without in 

 any way interfering with their enjoyment of life. The colora- 

 tion first appears in the vacuoles of the protoplasm, then this 

 latter is itself stained, the nucleus being most generally not at 

 tirst coloured, and so being made more conspicuous. Experi- 

 ments made on vegetable protoplasm seemed to exhibit the same 

 result. 



LARGE TELESCOPES^ 

 'T'HE small amount of work accomplished with large telescopes 

 ■*; has often been the subji'ct of unfavourable comment. This 

 criticism applies with especial force in America, where there 

 are nearly a dozen telescopes having an aperture of a foot or 

 over, besides two of the largest size now in course of construc- 

 tion, and two of twenty-six and twenty-four inches aperture 

 which are unmt unted and have been for several years perfectly 

 useless. Among so many it seems as if one might be spared for 

 a trial of the following plan, w-hich, if successful, would produce 

 at a small expense far more work than could be obtained with a 

 mounting of the u^ual form. 



Suppose that the telescope is placed horizontally at right 

 angles to the meridian, and that a plane reflector inclined to its 

 axis by 45° is placed in front of it. This reflector may revolve 

 around an axis coinciding with that of the telescope. .Such a 

 mounting has been used in transit instruments, and gives much 

 ^ By Edward C Pickering, communicated by the author. 



satisfaction in the meridian ))hotometer of the Harvard College 

 Observatory. The principal difficulty with a large instrument 

 would lie in the flexure of the reflector. This difficulty has how- 

 ever been overcome in a great measure in reflecting telescopes by 

 various ingenious devices. In the present case, since the 

 reflector rotates only around one axis instead of two, the 

 problem is much simplified. A slight motion at right angles of 

 perhaps 5° would be a great convenience, as will be shown 

 below, and w ould probably be insufficient to materially affect the 

 flexure. It may be said that it is more difficult to make a plane 

 surface than one that is curved. But the principal effect of a 

 slight curvature would be to change the focus of the telescope, 

 the aberration being much less than the effect of the varying 

 flexure. Let us admit, however, that the best definition cannot 

 be obtained, in considering the purposes to which such an 

 instrument could be applied without disadvantage. 



Many advantages will be apparent on comparing such a 

 mounting with an equatorial. Great steadiness would be secured, 

 since the mirror would be the only portion moved, and this 

 would be placed directly upon a low pier. Instead of a large 

 and exjjensive dome which is moved with difficulty, the mirror 

 would be protected by a small shed, of which the roof could be 

 easily removed. It would therefore be opened and ready for uss 

 in a very short time, and would quickly take the temperature of 

 the surrounding air. The objecl-glass would be mounted directly 

 upon a second pier, and, as it would not be moved, would be 

 in very little danger of accident. The tube could be made of 

 tin or other inexpensive material, as its flexure is of no import- 

 ance. It could easily be protected from the changes of the tem- 

 perature so troublesome in the tube of a large equatorial. If 

 preferred it might even he exhausted of air, or filled with hydro- 

 gen, and the effect of the changes of temperature thus greatly 

 reduced. 



The eyepiece could be mounted on a ihird pier, and would be 

 so far distant horizontally from the mirror and olject-glass that 

 there is no reason that it should not be inclosed in a room which 

 may be warmed. The comfort in winter of working in a warm 

 room will 1 :e appreciated by those w ho have used a large tele- 

 scope in a cold climate. The result is sure to be an increased 

 precision in tlie observation^, and a possibility of prolonging 

 them over longer intervals. A similar efiect is jiroduced by the 

 constant direction of the line of sight. No especial observing 

 chair is needed. There is no limit to the size of the attach- 

 ments which may be made to the eyepiece, since they need not 

 be moved. This is a great advantage in certain spectroscopic 

 and photometric measurements. A strong wind interferes 

 seriously mth many observations, as it is impossible to make a 

 telescope so stiff' that it will not be shaken by sudden gusts. In 

 the plan here proposed the mirror alone is exposed, and its sur- 

 face is too small to give trouble. 



By means of a long handle the position of the mirror may be 

 regulated from the eye-end, ai.d the declination of the object 

 observed read by small telescopes. If the mirror can be moved 

 at right angles to the meridian 5° from its central position, an 

 object at the equator may be follow ed for forty minutes, and 

 other objects for a longer period. Without this motion an object 

 may be followed for three or four minutes by moving the eye- 

 piece alcne. Clockwork may he applied to the mirror, or less 

 easily to the eyepiece. The focal length m.ay be increased almost 

 indefinitely if desired, and certain advantages will be thus 

 attained in the diminution in the defects of the object-glass, al- 

 thougli those of the reflector will not be aff'ected. If the telescope 

 is to be erected at a great elevation the advantages of the pre- 

 sent plan are at once apparent. Many nights of observation 

 would be secured which otherwise would be lost owing to the 

 w ind and cold. The simplicity in the construction of the build- 

 ing would be a great advantage, as a large dome in so exposed a 

 situation would be kept free from snow with much difficulty, 

 and might be a source of danger in winter storm*. If found 

 impracticable to observe during the winter, it would be possible 

 to have a duplicate mounting below, and remove the lens and 

 mirror from one to the other. 



It is evident that the saving of cost would be very great, not 

 only in the observatory building and dome, but in the tube, 

 observing chair, clockwork, &c. 



If a reflector could be constructed whose surface was the por- 

 tion of a paraboloid whose abscissa equalled that of the focus, 

 the instrument could be much simplified. No object-glass would 

 then be required, the reflector faking the place both of mirror 

 and lens. All the light intercepted by the objective w ould thus 



