58 



SCIENCE. 



[Vol. VII., No. 154 



early account ; another by Scott, in the Quarterly 

 journal of the royal meteorological society (i. 1873, 

 55-59), in which most of these references are men- 

 tioned. 



Further attention to the festoons is given in Poey's 

 little book, ' Comment on observe les nuages pour 

 prevoir le temps' (Paris, 1879, 86), and in Ley's 

 review of it in Nature (Jan. 1, 1880, 210). The 

 former calls it ' globo- cirrus ,' and traces its first 

 mention back to Lamarck in 1804 ; but Poey finds 

 only twenty records of the cloud that he can recog- 

 nize, seventeen of them being connected with storms. 

 Ley calls the festoons mammato- cumulus and mam- 

 mato-cirrus. figuring both kinds, and noting that 

 they are certainly not common, although not nearly 

 so rare as is usually supposed. Abercrombie notes 

 that the festoons result from the failure of the 

 ascensional current that is commonly associated with 

 showers and squalls (Nature, May 24, 1884). 



My object in writing is to ask if the cloud is com- 

 monly seen in this country, and if it is then generally 

 associated with the' cirro-stratus of thunder-storms, 

 or with the larger storms that are so unfortunate as 

 to have no special name, unless we call them ' areas 

 of low barometer.' My note books record the festoon 

 clouds twice in Montana in 1883, twice during the 

 past summer of 1885 in Connecticut and New York 

 (all these being in the cirro-stratus cover of the after- 

 part of thunder-storms), again here in Cambridge, 

 on Dec. 13, 1885, about noon, in the pallio-cirrus 

 sheet attending one of the above-named ' areas,' and 

 at a distinctly greater altitude than the low scud 

 and intermediate cirro-stratus clouds that soon closed 

 in, and gave us rain in the afternoon. They seemed 

 in all cases to be gently falling cloud-masses of 

 films, resembling the forms that ink may take when 

 dropped into water ; and, when watched attentively, 

 thej could be seen to descend and dissolve away. 

 Are they as rare as the notes by Symons and Poey 

 would lead us to think ? W. M. Davis. 



Cambridge, Mass., Jan. 5. 



Topographical models or relief-maps. 



I must personally thank you for vourgood words in 

 behalf of non exaggerated reliefs in your last issue, 

 p. 24. I have had a long experience in this kind of 

 work, and never found a case which required the 

 vertical scale to be exaggerated. No relief of the 

 surface is too delicate to escape the human eye when 

 represented with sufficient skill and care in model- 

 ling. The demand for exaggeration in a relief comes 

 from those who will not spend a sufficient amount 

 of time and pains upon the intermediate contour 

 curves, or from those who have not trained them- 

 selves in drawing from objects. The habit of 

 exaggerating the relief excuses itself at first on the 

 plea that common people cannot appreciate heights 

 when true to nature, but the fact is that the difficulty 

 is felt by the modeller himself ; and when the habit 

 is once formed, it becomes incurable. If a relief- 

 map be not true to nature, what is the good of it i 

 Geologists have been forced to abandon exaggerated 

 cross sections ; why should they permit relief-map 

 makers to revive the discarded error, and put the 

 representation of the whole in antagonism to the 

 representation of the parts ? 



Ahout the year 1865 or 180(5 I made a wooden 

 model of one of our lower Silurian limestone valleys, 

 with its bounding ridges, about 20 miles long. The 



model was about 18" by 36 ', in 12 bars of wood, each 

 18" long by 3" wide. On each side of each bar I 

 painted the corresponding section of the valley, with 

 its limonite horizons, and faults. The model still ex- 

 ists. My purpose was first to get correct ideas of the 

 country structure for my own work, and then to 

 exhibit my conclusions to the Pennsylvania railroad 

 company, who employed me. The reliefs in the val- 

 ley were very low ; but they were perfectly legible 

 to the eye of a layman. What would have been the 

 fate of my side-sections had I used an exaggerated 

 vertical scale ? 



In 1865 I made a model of the underground of the 

 Plymouth anthracite mine, with its remarkable ver- 

 tical fault, from levels which I took in the mine. 

 What good would this have been had I used a differ- 

 ent vertical scale ? 



I have myself made models on several plans ; the 

 most satisfactory, but the most laborious, being to 

 draw a good many cross-sections on the same vertical 

 and horizontal scale, along parallel lines, as nearly 

 as possible at right angles to the general strike ; then 

 cut strips of wood, lead, zinc, or stiff paper (I have 

 used all four) to represent the cross-sections ; set 

 these up in their places ; fill in with wax or plaster ; 

 and finally tool the surface thus obtained. I prefer 

 this method to the common one of jigging out the 

 contour curves, and filling the terraces between them 

 with slopes of wax. The latter method is easier and 

 less costly ; but it is sure to make the modeller slov- 

 enly in his geological representation, and it is a pow- 

 erful seduction towards exaggeration of the vertical 

 scale. Beginners and earnest scholars ought not to 

 be allowed to use this method until they have been 

 drilled to accuracy, and to love the true natural 

 aspect, by the compulsion of the method of cross- 

 sections. I never see a false relief-map without 

 indignation, and a touch of the contempt we feel for 

 all anachronisms. J. P. Lesley. 



Philadelphia, Jan. 10. 



The cherry tortrix. 



This insect, Cacoecia cerasivorana Fitch, was very 

 common in Michigan the past summer. The most 

 interesting thing about it is the large web or tent 

 which it spins, and in which it usually stays. As 

 it needs more food, it ' ropes in ' new twigs, and thus 

 has fresh foliage right at hand. I found that these 

 little caterpillars would deflect a shrub, an inch or 

 more in diameter, several inches, that its leafy 

 branches might be brought into its tent. How do 

 these little larvae exert so much force ? I know that 

 entomologists usually say it is by the pulling of the 

 hundreds of larvae as they move their heads back 

 and forth in the operation of spinning ; but I do not 

 see how they can pull. As they touch their mouth 

 to the web or twig, the liquid secretion adheres, and 

 quickly hardens into a tough thread ; but the larvae 

 do not seem to draw, nor is it certain that the thread 

 would be strong enough so early in its formation to 

 draw with any force. From very careful observation 

 in the laboratory, I was led to believe that it was due 

 to the contracting force of the many hardening silk 

 threads that brought the large twigs together. These 

 larvae are smooth, and must find the web a great 

 protection. The teeth on the chrysalides are of great 

 service in enabling them to push out of the tents, 

 just as the moths are to issue. A. J. Cook. 



Lansing, Mich. 



