September 9, 1897] 



NATURE 



453 



committing itself upon the much more difficult question of 

 their precise age. 



In a previous note in Nature (p. 205), attention was called 

 to Dr. Giovanni Vailati's studies on the statical notions of 

 Archimedes. We have now received a reprint of a further 

 paper by the same writer {Atiidella R. Accademia delk Scienze di 

 Torino^ xxxii.), dealing with the " Principle of Virtual Work 

 from Aristotle to Hero of Alexandria." From an examination 

 of the Mechwiika Problemata of Aristotle, the Barotilkos of 

 Hero, and a Latin thirteenth century manuscript, De pottdertbus, 

 attributed to Giordano Nemorario, it appears that this principle, 

 though commonly supposed to have been discovered about the 

 end of the fifteenth century, was in reality known to the Greeks. 

 In the work of Hero, Dr. Vailati finds not only distinct state- 

 ments of the relations between forces and the displacements 

 produced by them, but also applications of the principle to 

 various machines, including pulleys. From this evidence the 

 author attributes to the Greeks a knowledge of the subject con- 

 siderably in advance of that evinced by the sixteenth-century 

 writers on statics. 



A PHOTO-VOLTAIC theory of photographic processes forms 

 the subject of a lengthy investigation, by H. Luggin {Zeitschrift 

 fu7- physikalische Chemie, xxiii. 4). It was shown by Becquerel, 

 in 1839, that the haloids of silver are capable, under certain 

 conditions, of giving rise to photo-voltaic currents ; and Herr 

 Luggin finds a close connection between these currents and the 

 decompositions which give rise to photographs. A remarkable 

 feature is the reversal of the voltaic current which occurs when 

 a certain potential has been reached, a consequence of which is 

 that the same electrode is capable, according to circumstances, 

 of giving rise to currents of opposite signs, and these Herr 

 Luggin distinguishes as "normal" and " solarisation currents." 

 The former are the more susceptible to blue, and the latter to 

 yellow light. The whole investigation tends to throw light on 

 the much-debated theories of photographic action, by showing 

 that both the latent picture of photographic negatives and the 

 visible transformations of the printing-out process have their 

 counterpart in definite photo-voltaic phenomena. 



An interesting account of the earthquake of Aidin (Asia 

 Minor) on August 19, 1895, is given by Dr. G. Agamennone in 

 Gerland's Beitrdge zur Geophysik. The epicentre is situated at 

 or close to the village of Imamkeuy, which is 6 km. east of 

 Aidin, and the majority of damaged buildings lie within an area 

 about 50 km. long and 20 km. broad, the longer axis of the 

 area being roughly parallel to the valley of the Menderes. The 

 disturbance was registered by the Vicentini microseismograph 

 at Padua (1570 km. from the origin), and the horizontal 

 pendulum at Strassburg (2010 km.). The usual secondary 

 phenomena, such as landslips, fissures in the ground, and the 

 derangement of the underground water-system, occurred in the 

 epicentral area ; and some of the landslips gave rise to thick 

 clouds of dust, which hung in the air for several hours, and were 

 then carried by the wind to the south side of the valley and 

 deposited on the adjoining mountains. 



We have heard often enough that loud and continued explo- 

 sions produce rain, and the recollection of rain-making experi- 

 ments based upon this apparent connection is still with us. 

 Now comes a report from Mr. Germain, United States Consul at 

 Zurich, on the prevention of hailstorms by the same means 

 that have been used to encourage a downfall of rain. It appears 

 that Mr. Albert Stiger, burgomaster of Windisch-Freistritz 

 (Lower Steirmark, Austria), owns extensive vineyards situated 

 on the southern slopes of the Bacher Mountains, a locality often 

 visited by destructive hailstorms. To protect his vines from 

 hail, he decided to try the shooting or explosive system to 

 NO. 1454, VOL. 56] 



scatter the clouds and drive away approaching hail or heavy 

 rain storms. Six stations were therefore erected on the six 

 most prominent summits surrounding the locality, and command- 

 ing a territory of about two miles in extent. These stations 

 sheltered ten heavy mortars each. Upon the slightest indication 

 of a storm the mortars were immediately manned and loaded with 

 120 grams of powder each — about 4^ ounces— and shooting com- 

 menced simultaneously and continued regularly out of the sixty 

 mortars until the clouds were scattered and the storm had blown 

 over. These experiments were anxiously watched by the citizens 

 of Windisch-Freistritz last summer. Threatening black clouds 

 made their appearance over the summits of the Bacher Moun- 

 tains ; at a given signal all the mortars were fired off, and the 

 continuous detonations in a few moments caused a sudden 

 reaction in the movements of the clouds. It is said that the 

 cloud opened up funnel-like, the mouth of the funnel began to 

 rise in the form of consecutive rings, expanding gradually until 

 all of the cloud scattered and entirely disappeared. There was 

 no hail, or even a sudden downpour of rain. The same ex- 

 perience was gone through six times during the summer, and 

 proved a successful preventive in each case. We await the views 

 of Austrian meteorologists upon these experiments ; meanwhile, 

 rain-makers who have put their trust in explosions must hide 

 their diminished heads before the rain-dispersers. 



It has long been known that in the Pondicherry district of 

 Peninsular India there occur Cretaceous rocks with a peculiar 

 fauna, but though studied by such palaeontologists as Forbes, 

 d'Orbigny, and Stoliczka, the exact horizon of these beds has 

 remained uncertain, they having been variously placed in the 

 lower, the middle, and the upper parts of the Cretaceous system. 

 This question may be taken as finally settled by Dr. F. Koss- 

 matt {Records Geol. Survey India, xxx. 2, May 1897), who, 

 applying the increased modern knowledge of the succession of 

 life-forms in the Cretaceous to these beds, divides them into 

 three divisions, of which the two lower represent the Upper 

 Senonian (highest part of the English chalk) and the upper the 

 Danian. The general interest of Dr. Kossmatt's paper lies, 

 however, in the side-issues which it raises. Similar beds are 

 known in Natal, Madagascar, Assam, Borneo, Yesso, Vancouver 

 and Quiriquina Island, Chili. The similarity of the fauna in 

 these beds shows the Pacific Ocean to have formed a well-defined 

 province in Cretaceous times, separated by a barrier from the 

 Mediterranean Ocean which extended through Europe and 

 Central Asia. Somewhere in the Atlantic area, however, this 

 barrier was imperfect, and a migration of Pacific forms into the 

 Mediterranean took place, and a reverse migration to a smaller 

 extent. By a careful study of these forms. Dr. Kossmatt arrives 

 at a number of interesting conclusions : (i) The time required 

 for the dispersal of a species was insignificant beside the time 

 required for a measurable amount of sedimentation, so that in 

 this case homotaxis means contemporaneity. (2) As the 

 Ammonites were dispersed, they underwent definite specific 

 changes, so that their wide distribution as fossils cannot be 

 explained as the result of the flotation of their dead shells, as has 

 been suggested by Dr. Walther. (3) The Ammonites seem to 

 have possessed greater capacity for distribution than other 

 groups. (4) The appearance of a new fauna in several cases coin- 

 cides, everywhere, with an overlap, indicating an extension of the 

 ocean over the land-surface : this repeated " positive displace- 

 ment " of shore-lines is as characteristic of the Cretaceous all 

 over the world, as the opposite displacement is of the beginning 

 of the Tertiary ; the Pondicherry beds, for example, rest directly 

 on the Archjean crystallines of the Peninsula. 



The latest number of the Journal of the Asiatic Society of 

 Bengal (vol. Ixv. part II. No. I, 1897, p, 345) is entirely taken 

 up with the ninth descriptive catalogue of " Materials for a 



