333 



SCIENTIFIC NEWS. 



[Sept. 28, 1888. 



millimetre of length the surface of water experiences a 

 tension of 7'S milligrammes. Let us imagine a surface 

 of water of one square millimetre, and ask what work 

 must be expended in order to double this surface of one 

 square millimetre. We have to overcome a series of small 

 forces the sum of which is 7-5 milligrammes, and to cause 

 all the points of application of these elementary forces 

 to describe a track equal to one millimetre. But as the 

 work is exactly equivalent to the product of the intensity 

 of the force of the track traversed upon the right line 

 where the force exists we have to effect here a work of 

 7 '5 milligrammes-millimetres. This work expended will 

 be found as available energy in the new square milli- 

 metre of free surface ; it is this energy of 7 '5 milli- 

 grammes-millimetres which I have called the potential 

 energy of pure water. We must not forget that this 

 energy resides in a layer of not more than ^-^ millimetre 

 in thickness. We thus comprehend than in the surface 

 layer of the ocean there is stored up a mechanical power, 

 of which nothing can give an exact idea. 



I suppose now that of two surface layers, equal and in 

 juxtaposition, the one glides over the other by the action 

 of the wind. The layer which is completely covered, 

 will have lost its free surface, and with it its characte- 

 ristic potential energy. If the sliding is effected slowly, 

 this energy will be replaced by an equivalent quantity 

 of heat. But if the phenomenon takes place rapidly the 

 lost potential energy gives rise to an increase of speed. 

 If, therefore, the wind communicates to certain layers of 

 the sea a greater velocity than it does to the neighbour- 

 ing layers, the latter are covered by the former which in 

 turn cover others more remote, and so on. This is why 

 each wave in the course of formation is composed of 

 portions whose velocities are greatest towards the top. 

 When the wind is violent the acceleration of velocity 

 produces upon each wave a crest which becomes more 

 and more prominent, and which finally breaks. 



Hence it follows that any cause which prevents the 

 sliding of superficial layers of the waters of the sea oae 

 over the other, will constitute an obstacle to the gradual 

 increase of the vis viva of the liquid masses. 



But just such a cause is found in oil which covers the 

 surface of the sea over a sufficient extent ; in virtue of 

 its low specific gravity it always rises to the surface 

 and renders the sliding of one layer over the other im- 

 possible. This explains the seemingly mysterious effi- 

 cacy of oils capable of being spread out in films of an 

 incredible thinness (1-100,000 to 1-200,000 of a milli- 

 metre). As soon as this sliding of the layers is prevented 

 the formation of the breakers so dreaded by ships is 

 rendered impossible. 



Further, this action of oils transforms crested waves 

 into an even swell, as was pointed out even by Aristo- 

 teles, Pliny, and Plutarch. 



The author, Professor Van der Mensbrugghe concludes 

 his memoir with regretting that the use of oil at sea is not 

 studied in Belgium. 



EXPLORATION IN MOROCCO. 



"pROM communications received from Mr. Thomson, 

 dated from the city of Morocco, July 22nd, it 

 appears that by a series of surprises and cleverly- 

 planned excursions he has been able to enter the 

 mountain fastnesses of Morocco and do more than any 

 previous traveller has done. From Demnat he made 

 two extremely interesting trips into the lower ranges, 



visiting some remarkable caves and equally remarkable 

 ruins, and one of the most wonderful natural bridge- 

 aqueducts in the world. Geologically and geographically 

 these trips are alike important. This was followed by 

 a dart across the main axis of the Atlas to the district of 

 Tiluit, which lies in the basin of the Draa. As the 

 tribes further west on the southern slope were in revolt, 

 Mr. Thomson was compelled to return to the northern 

 plains. Starting once more, he crossed the mountains 

 by a pass a little south of Jebel Tizah, ascended by 

 Hooker, and reached Gindafy safely. He was able to 

 make a trip up a wonderful canon, which he declares 

 rivals those of America for depth and grandeur, and as- 

 cended a mountain, where he and his party were con- 

 fined to their tents until it suited them to go back to 

 their starting point. Here Mr. Thomson's companion, 

 Mr. Crichton Browne, was stung by a scorpion, and they 

 were compelled to return by a new route. 



From his previous starting point Mr. Thomson scored 

 another great triumph. He crossed the mountains 

 once more, and ascended with no small danger and 

 difficulty the highest peak of the Atlas range north of 

 Amsiviz, a height of 12,500 — the highest peak by 1,500 ft. 

 ever attained. 



In a few days after the date of his letter Mr. Thomson 

 intended to resume work. He proposed to make for the 

 Urika river and penetrate the mountains up its course, 

 then work his way round to Mogador, which he expects 

 to reach about the end of August. He may then make 

 one or two short trips into the interior and down to 

 Agadir. The return route to Tangier will probably be 

 from Mogador to the city of Morocco, thence to Mazagan 

 on the coast, and on to Casablanca and Rabat. Then he 

 will leave the sea again and go to Mequinez and Fez, 

 reaching Tangier about the end of the year. 



*-£t£*g+^-* — 



NOTES ON ESSENTIAL OILS. 



T T OP oil, distilled from Bavarian hops, has now dis- 

 placed that prepared from lupulin, which it excels 

 in richness and delicacy of odour, due to the absence of 

 butyric and valerianic acids. It is a mistaken notion 

 that this oil has narcotic properties. 



Marjoram oil, from Spain, recently introduced into 

 commerce, differs essentially from the oil distilled from 

 German marjoram. It is recognized by its freedom from 

 colour. 



Pepper oil, used extensively in fortifying spices, is 

 obtained as a by-product in the manufacture of piperonal 

 (heliotropin). 



Rose oil and rose water have been recently produced 

 in limited quantities experimentally in Germany, near 

 Leipsic. It is said that there are now under cultivation 

 for this purpose 15 acres of land, and the results have 

 been quite satisfactory. The German oil is superior to 

 any imported. It congeals at 20 (68° F.), showing the 

 presence of a larger proportion of the fragrant stearop- 

 tene than is contained in the best Turkish oil. 



Betel leaves yield an essential oil (0-5 per cent.) of a 

 brown colour, an agreeable, tea-like odour, and a 

 burning taste. Its specific gravity is 1-020 at 15 C. 

 It boils at 250° to 260 C., and consists of a phenol 

 agreeing in properties and reactions with eugenol and 

 an indifferent hydrocarbon. The leaves are used in 

 India in catarrhal and pulmonary affections, and it is 

 probable that they owe whatever therapeutic virtue 

 they have to the essential oil. 



