September 29, 1893.] 



SCIENCE. 



179 



wrapping paper and cord to secure this trophy of the 

 past, and draw from it its inmost secrets. The grinding 

 is simply friction with emery and water till the first face 

 IS prepared, and polished on the chamois skin with dry 

 emery slime. This should be as perfectly done as possi- 

 ble. The specimen may be considered as finished at this 

 stage, if no com2?lete examination of structures is intended, 

 no tracing of homologies in various genera and species. 

 If this exact study is to be prosecuted, on one of the 

 small glass jjieces, polished surface down, imbed the 

 specimen in balsam, just hard enough and deep enough 

 to securely hold it, but not so hard as to crack off, as the 

 grinding of the second surface advances. Care must be 

 taken to hold the glass horizontally, lest the specimen be 

 of unequal thickness at the close. When nearly translu- 

 cent, great care must be taken by grinding lightly and 

 more and more lightly, till the work is complete and the 

 polishing done. Warm the balsam which still holds it 

 to the glass, and delicately sUde the well-earned treasure 

 to a new microscopic slide, 1x3 inches, on which 

 is a drpp of hot balsam. This successfully done, remove 

 any air bubbles and lay on the cover glass, removing 

 bubbles again. Clamp it with a clothes pin till dry and 

 cold, then remove all surplus balsam with turpentine, 

 taking care that it does not also run under the cover 

 glass. It is now ready for study. When several speci- 

 mens of different sisecies or genera of Rugosa, for in- 

 stance, have been made, fine lessons may be drawn in 

 homologies, especially of mural, septal and tabular sys- 

 tems. 



As the large majority of students wiU not carry their 

 scientific studies, as such, farther than the requirements 

 of the college curriculum, it is eminently important that 

 their attention be called all along to certain prominent 

 things as prominent, as the great questions to be sought 

 out. In giving these special points of the field in general, 

 the teacher or professor will naturally present in a more 

 extended way that special field which has most attracted 

 his or her own attention or investigation. For reference 

 and for present benefit the pupils should each, under the 

 eye of the teacher, make a geological map of the United 

 States; one of his own state on a larger scale, and of his 

 own section on a still larger one. He should also 

 number carefully and permanently his specimens, using a 

 tiny circle of paper and glue unaffected by ordiuary 

 moisture, these numbers corresponding to those on labels 

 bearing name of formation, group, genera and species, 

 with the date and locality. 



In preparing this paper I have been painfully conscious 

 of its inadequacy and its great imperfections, yet from 

 experience and observation I hope to have measured an 

 arc in the circle of scientific and geologic education in 

 our schools whose circumference may be eventually com- 

 pleted. 



LETTERS TO THE EDITOR. 



^^Correspondents are requested to be as brief as possible. The 

 writer's name is in all cases required as a proof of good faith. 



On request in advance, one hundred copies of the number con- 

 taining his communication wiU be furnished free to any corres- 

 pondent. 



The editor will be glad to publish any queries consonant with 

 the character of the iournal. 



An Instructive Illusion. 



On Thursday evening. May 18th, occurred at York one 

 of those smart thunder-showers which followed the break- 

 up over the greater part of England of the sunniest, warmest 

 and driest spring within the memory of mosti Hail 

 had fallen, and five minutes later, at 6.50, clear sky appeared 

 among the storm-clouds. Not quite clear, however, for it was 

 flecked with those very delicate, filmy, white clouds which 

 one usually assigns to a very lofty altitude. The sun 



being within an hour of setting, its slanting rays illu- 

 minated these strongly. It was therefore with surprise 

 that I saw shoot athwart these sharply-defined, intensely 

 dark bars of shadow. These evidently came from a por- 

 tion of cumulus-like thunder-cloud, which topped the 

 main mass just below and to the right of the new moon. 

 Some of the rays sprang direct from its edge, but others 

 at a distance of 2° to 10°. In the shadow the filmy 

 clouds were absolutely invisible, the sky seemingly being 

 of a clear blue, although the shifting of the bars of 

 shadow indicated their actual presence everywhere. 



T^S.HAOOW~l'^CONTAC-r WITH "CLOUD. 



.THE -bTRAIGHT 



But the strange question arises, what was the real 

 height of the film-clouds? Must they not, obviously, 

 have been at a lower level than this portion of the thun- 

 der-cloud, though higher than the main mass ? And yet 

 portions must have been piled higher against the thun- 

 der-cloud. Else there could not have been the illuminated 

 space dividing the shadow from the cloud. In some 

 cases the dark bars merged into sheets of shadow, which 

 stretched away 20° or more from the cloud. Apparently, 

 if seen in section, the effect must have been as in the ap- 

 pended sketches. 



It is diificult to conceive any other explanation than the 

 above. Hence, either siich film-clouds form at lower 

 levels than is generally supposed, or the summits of 

 thunder-clouds penetrate higher than has been supposed. 



J. Edmund Cl.a.bk. 



Why Not the Collections of Seeds ? 



In these days of stamp, coin, shell, mineral, plant and 

 insect collectors, the writer has often wondered why 

 it is that so few have turned their attention to 

 making collections of seeds. The field, as it apjsears 

 to me, is one of exceptional interest; exceptional not 

 merely because of the work of real merit that may be done 

 therein, but because it is practically inexhaustible; be- 

 cause the materials are very largely of such a nature as to 

 be cared for with a minimum amount of labor, and re- 

 quire but little sfiace; and because in many instances seeds 

 are themselves objects of great beauty. There are few 

 pursuits in which greater latitude may be allowed, or 

 greater opportunity is given for display of individual 

 energy and mental scope. The amateur, whether man or 

 woman, boy or gu-1, business man or teacher, crijjjjle or 

 invalid, may each and all collect and find ample room for 

 so much or so little study as he or she may choose to de- 

 vote to it. One may collect only such seeds as have in 



