202 



SCIENCE. 



[Vol. II., No. 28. 



in the manner of a skein of thread." I do not Ijnow 

 of any explanation of the use of these tliieads. Can 

 any of your readers suggest a purpose for them? 



Jos. F. James. 



Cincinnati, O., Aug. 2, 1883. 



Seeds of Lcpidium. 



I regret to observe, by your issue of July 27, that 

 my employment of the expression 'mucilaginous 

 threads' as to tlie seeds of Lepidiura has led your 

 reviewer to understand tliat I referred to something 

 like the seed-fibres of Collomia. Spiral fibres em- 

 bedded in mucilage are found on the seeds of Col- 

 lomia; radiating processes consisting of mucilage, 

 each tipped by a facet of cuticle, are emitted by the 

 seeds of Lepidium virginicum. Tbis is shown on the 

 application of water with staining-tiuid to ripe seeds. 

 Other species of Lepidium (including L. ruderale) 

 show the same phenomenon, though the experiment 

 may fail with immature'Seeds or olil herbarium speci- 

 mens. G. Macloskie. 



Princeton, N.J., Aug. 3, 1883. 



["The exotest may bear long hairs (cotton) or 

 spiral threads. ... In Lepidium (pepper-grass), on 

 being moistened, it darts out mucilaginous threads " 

 It certainly may be gathered from this that the 

 ■ spiral threads ' and the ' mucilaginous threads ' are 

 not the very same. But tlie darling-out of muci- 

 laginous threads so well describes what one sees in 

 Collomia-seeds and the like, and so poorly answers 

 to what takes place in those of Lepidium, that the 

 reviewer supposed there miglit be some mixing up 

 of cases. But lie simply aske<l whether the autlior 

 ■was sure of the threads in Lepidium. We find nothing 

 to which the name of 'mucilaginous threads' can 

 with any exactness be applied; nor do we think that 

 the term now used of ' radiating processes,' though 

 not widely amiss, gives a clear idea of the case, 

 which we should describe thus: — 



A superficial pellicle of the seed-coat of Lepidium 

 consists of a single and continuous layer of cells, 

 the thick walls of which are at matuiity couveited 

 itito mucilage, or into an isomer of cellulose, which 

 swells up into mucilage 'upon the application of 

 water.' But the water acts so promptly in forming 

 the liinhus around the seed or its section, that we fail 

 In that way to get an intelligible view of the structure 

 and tlie nature of the' process. To do this, however, 

 we Iiave only to soak thin sections of the seed in 

 strong alcohol, examine in. them the unaltered muci- 

 lage-cells, and then add a little water by degrees. 

 The cells tlien swell up slowly, pusli outward radially 

 (for mutual pressure prevents lateral expansion at 

 the beginning), become wedge-shaped or pear-shaped 

 as they farther protrude, and at length form the 

 well-known mucilaginous llinhuis. Dr. Macloskie 

 will be interested in repeating this experiment, and 

 will accept our apology for partially misunderstand- 

 ing him. J 



KONKOLY'S ASTRONOMICAL INSTRU- 

 MENTS. 



Praklisclie cmleitung zur ansteUunq astronomhchen 

 beohachhtngen, mit hesonclercn rilcksicht avf die 

 nstrophynik, nehst einer morlernen instruvienteu- 

 kunde. Von Nicolaus von Konkoly. Braun- 

 schweig, Vieweg, 1883. 912 p., 315 illustr. 8°. 



This is an important but at the same time 

 a disappoiutiug work. It contains the descrip- 



tion and representation of nearly all the prin- 

 cipal modern astronomical iu.struincnts, and 

 presents such a comprehensive summary as 

 can be found in no other existing book. The 

 numerous ilhistralioiis, largely derived from 

 the business catalogues of leading instru- 

 ment-makers, are generally excellent, and the 

 mechanical execution and press-work are ad- 

 mirable. Undoubtedlj- the book is one which 

 must have a place in everj' astronomical library. ' 



At the same time, the work is far from ex- 

 haustive, omitting all mention of many of the 

 latest and most useful impi-ovenients ; and it 

 is not always accurate in its descri|)tion of 

 those it does notice. Nor does it deal in any 

 thorough or satisfactory manner with the theory 

 of the instruments described. It is so full and 

 so good, that it is a great pity that it is not 

 still better and still more complete, as it easily 

 might have been. 



The first chapter, on time-keepers (uhren), 

 describes, among clock-escapements, onlj- the 

 old Graham dead-beat and a duplex of Jiirgeu- 

 seu's. There is no notice of Aity's detached 

 escapement, now in use at Greenwich, nor of 

 anj- of the numerous and excellent gravity- 

 escapements now so common in England and 

 this country. The account of electric make 

 and break circuit apparatus is for this reason 

 unsatisfactory, since only escapements of the 

 detached class admit of a simple break-circuit 

 which does not afiect the pendulum. The 

 author treats the subject rather extensively, 

 describing no less than twelve ditferent forms 

 of contact apparatus, some of them very elab- 

 orate and complicated. The antiquated con- 

 trivances of Locke and Mitchell are described 

 as if they continued to be in use. 



The second chapter, a short one, deals with 

 the ditferent forms of levels and level-testers, 

 and appears to be in all respects satisfactory. 



The third chapter treats of instruments for 

 the determination of time. Under this head 

 are incltided not only transits and transit-cir- 

 cles, but all forms of theodolites, sextants, 

 passage-prisms, etc. There is also a certain 

 amount of information respecting the gradua- 

 tion of circles and the methods of testing their 

 accuracy, i.e., the optical and mechanical ar- 

 rangements ; the mathematical theorj- remain- 

 ing untouched. 



The next chapter, the fourth, is by far the 

 most extensive and full of an}-, occupying two 

 hundred and forty-six pages. It treats of 

 eqtiatorials and their mounting, and describes 

 and illustrates nearly- all the important modern 

 telescopes. For the most part, it is well done, 

 especially the portion relating to driving-clocks. 



