530 



NATURE 



{April 1^, 1877 



solid body, the currents mentioned above with reference to the 

 iron must necessarily be far less strong. 



"With similar modifications according to the temperature 

 required for their liquefaction the swimming takes place vfith all 

 other metals." 



Tycho Brahe's Portrait 



In Nature (vol. xv., p. 406) is published a copy of a portrait 

 of Tycho Brahe in the possession of Dr. Crompton of Man- 

 chester. Although it seems, from the inscription in the corner, 

 that the portrait is a contemporary one, there does not appear 

 to me to be sufficient reason for preferring this portrait, of the 

 origin of which nothing whatsoever is known, to others of the 

 same date. Both Tycho's " Epistolse " and " Mechanica " con- 

 tain an engraving by J. D. Geyn from the year 1586, and if the 

 newly-discovered portrait really (as conjectured by Dr. 

 Crompton) should have been painted to be engraved for the 

 " Mechanica," it can hardly have been considered a good like- 

 ness, as the engraving by Geyn was preferred. The latter is 

 very like the portrait on Tycho's large wall-quadrant, of which 

 an engraving in the " Mechanica" gives us an idea, and which 

 Tycho himself mentions with the following words : — " llanc 

 effigiem magna solertia expressit Thobias Gemperlinus eximius 

 art'fex (quem mecum Augusta Yindelicorum in Daniam olim 

 receperam) idque tam competenter, ut vix similior dari possit." 

 This portrait is from 1587. 



The Royal Gallery at Frederiksborg (about twenty English 

 miles from Copenhagen) contained a fine portrait of Tycho 

 Brahe, which unfortunately was burned in the great fire in 1859, 

 when so much of that beautiful castle was destroyed. It agreed 

 on the whole with the two above-mentioned portraits, while the 

 long narrow face on the Manchester portrait shows hardly any 

 resemblance to the features on the others. I may also add, that 

 the fine monument erected by Tycho Brahe's heirs in the church 

 in Prague (Teinkirche), where he was buried (of which I have 

 seen a copy in Copenhagen), is very like Geyn's and Gemperlin's 

 engravings. 



The article which accompanies the portrait in Nature con- 

 tains several small mistakes, which perhaps also occur in 

 Brewster's " Martyrs of Science." Tycho was not born in 

 Sweden but in Denmark, as the province of Schonen (with the 

 island of Hven) belonged to the latter country from ancient 

 times and up to 1660, and he was of an ancient Danish noble 

 family. His castle was called *' Uraniborg " (Latin Urani- 

 burgum, the Celestial Castle), the Observatory "Stjerneborg" 

 (Stellseburgum). J. L. E. Dreyer 



Observatory, Birr Castle, Ireland 



Yellow Crocuses 



Can any of your readers elucidate this problem ? When, a 

 fortnight ago, the yellow crocuses flowered, the sparrows all at 

 once made a terrible onslaught upon them. I found the gardener 

 in Lincoln's Inn Gardens one day mourning over a fine line of 

 crocus plants, every flower of which was in absolute ruins. All 

 the work of the sparrows, he said. I ^have seen them, too, on 

 the flower-boxes in my windows here frequently, tearing at the 

 crocus blooms. Yet now, later, the blue and striped crocuses 

 are blowing, and the sparrows leave them altogether untouched. 

 What is there in the London bloom specially that attracts the 

 London sparrow ? The taste is, I think, peculiar to the town 

 bird. In gardens at a distance from, and immediately around, 

 London, I have watched plenty of yellow crocus blossoms, not one 

 flower of which has been attacked. 



Gray's Inn, April 6 Alfred George Renshaw 



Tropical Forests of Hampshire 

 In Mr. J. Starkie Gardner's lecture on The Tropical Forests 

 of Hampshire (Nature, vol. xv. p. 232), the following state- 

 ment occurs which is open, I think, to considerable question : — 

 ' ' All the shipworms generally known to us live only in salt- 

 water, and are so delicately organised that the slightest mixture of 

 fresh-water instantly kills them." This sweeping assertion is 

 partly qualified by allusion to the occurrence of a species described 

 by Mr. George Jeffries as inhabiting fresh-water, and the fact of 

 bored wood being found 300 miles up the Gambia River ; still 

 as Mr. Gardner speaks ol these facts as a " theory" still in need 

 of verification, I would point out that no waters are more infested 

 with the shipworm than the deltas of tropical rivers wherein the 

 water is often largely brackish if not potable. 



My own experience is confined to the delta of the Irawadi, a 



tangled maze of creeks, the waters of which are brackish or salt 

 for about a third of the year, and slightly so, and even potable, 

 during the other months. The large canoes, however, which 

 traverse these creeks are much injured by some species of ship- 

 worm, and so little does the easy remedy of exposing them to 

 fresh-water answer, that the Birmese are in the habit of firing 

 their bottoms from time to time ; opportunity is taken of a high 

 spring tide to get the boat well on shore. The ends are sup- 

 ported on blocks of wood, and a shallow saucer-shaped cavity is 

 made underneath which is filled with straw or other combustible 

 matter, which gives a fierce but short-lived flame. Fire is now 

 applied and the bottom of the boat is for some minutes kept 

 wrapt in flame, which steams the worms to death in their holes. 

 I cannot recall any instances of bored wood well above the tide- 

 way, but wherever the water is occasionally brackish, thus far 

 the worins seem capable of settling. What species occur in 

 Pegu I cannot say. Percival Wright has described Nausitora 

 dunlopei from the rivers of Eastern Bengal, and it may not im- 

 probably extend to the Irawadi delta, as Novactdina gangetica 

 and a species of Scaphula closely allied to the Gangetic species 

 do. The two Birmese species of Scaphula are both estuary 

 forms, whereas the type of the genus in the Ganges is found a 

 thousand miles fr>,m the Jea, which suggests the plasticity of 

 some species, which if met with fossil would be unhesitatingly 

 regarded as marine. W. Theobald, 



Camp, Jhilum District Geological Survey of India 



Hog Wallows or Prairie Mounds 



In Nature (vol. xv., p. 274), Mr. Wallace quotes a letter 

 from his brother in regard to the so-called Hog-wallows of 

 California, in which their origin is ascribed to debris left at the 

 broad foot of a retiring glacier modified by the erosion of innu- 

 merable issuing rills, and asks if this structure is known to occur 

 elsewhere. As I have observed the same formation in many 

 parts of the Pacific slope and have tried to explain it, I hope 

 I may be allowed to say a few words on the subject. 



The peculiar configuration of surface so well described by Mr. 

 Wallace, is very widely diffused in America, and has been 

 described under different names. In California the mounds are 

 called Hog-ivallows, but elsewhere they are known as Prairie 

 mounds. Tfiis latter is the better name since they are found 

 only in grassy, treeless, or nearly treeless regions. They occur 

 over much of the Prairie region or "plains^' east of the Rocky 

 Mountains; also over portions of the basin region, e.g., in Ari- 

 zona ; also over much of the bare grassy portions of California, 

 e.g., along the lower foothills of the Sierra and adjacent por- 

 tions or the San Joaquin plains ; also over enormous areas in 

 Middle Oregon, on the eastern slope of the Cascade mountains, 

 an undulating grassy region ; also on the level grassy Prairies 

 about the southern end ot Pugit Sound, Washington territory. 



They have been ascribed to the most diverse causes. In Texas, 

 where they are very small. Prof. Hilgard thinks they are ant- 

 hills. In Arizona, where they are also imperfectly developed, 

 Mr. Gilbert thinks they are the ruined habitations of departed 

 Prairie dogs. In some portions of California, also, where they 

 are small, they have been popularly ascribed to hiu-rowittg squir- 

 rels. In the Prairies, about Pugit Sound, where they are splen- 

 didly developed, their great size and extreme regularity has 

 suggested that they are burial mounds, and that the Prairies are 

 veritable cities of the dead. It is possible that the cause may be 

 different in different places, but I am sure that no one who has 

 examined them in California, and especially in Oregon and 

 W^ashington, can for a moment entertain any of these theories 

 for the Pacific slope. 



In a paper " On the Structure and Age of the Cascade Moun- 

 tains," published in the American Journal iox March and April, 

 1874, p. 167 and p. 259, among some miscellaneous points 

 suggested by the main subject in hand, I discus-s this one of Prairie 

 mound. I there attribute them to surface erosion under peculiar • 

 conditions, these conditions being a bare country and a drijt-sotl 

 finer and more tnovable above and coarser and less movable below. 

 Erosion removes the finer top-soil, leaving it only in spots. The' 

 process once commenced, weeds and shrubs take possession of 

 the mounds as the best soil, or sometimes as the driest spots, and 

 hold them, preventing or retarding erosion by their roots. In 

 some cases, perhaps in most cases, a departing vegetation, i.e., a . 

 vegetation gradually destroyed by increasing dryness, seems to 

 be an important condition. For my full reasons for holding this , 

 view I must refer the reader to my paper, but I may say \Si%- 

 passing that in the bare hilly regions of Middle Oregon, on the,^ 



A 



