Page:EB1911 - Volume 27.djvu/930

 The values of the co aggregation-volume c, which form the starting-point of the calculation, are found by taking n=10/3 for convenience of division in formula (13). The unit of heat assumed in the table is the calorie at 20° C., which is taken as equal to 4·180 joules, as explained in the article. The latent heat L (formula 9) is found by subtracting from H (equation 15) the values of the heat of the liquid h given in the same article. The values of the specific heat in the next column are calculated for a constant pressure equal to that of saturation by formula (16) to illustrate the increase of the specific heat with rise of pressure. The specific heat at any given pressure diminishes with rise of temperature. The values of the saturation-pressure given in the last column are calculated by formula (25), which agrees with Regnault's observations better than his own empirical formulae. The agreement of the values of H with those of Griffiths and Dieterici at low temperatures, and of the values of p with those of Regnault over the whole range, are a confirmation of the accuracy of the foregoing theory, and show that the behaviour of a vapour like steam may be represented by a series of thermodynamically consistent formulae, on the assumption that the limiting value of the specific heat is constant, and that the isothermal are generally similar in form to those of other gases and vapours at moderate pressures. Although it is not possible to represent the properties of steam in this manner up to the critical temperature, the above method appears more satisfactory than the adoption of the inconsistent and purely empirical formulae which form the basis of most tables at the present time.

A similar method of calculation might be applied to deduce the thermodynamical properties of other vapours, but the required experimental data are in most cases very imperfect or even entirely wanting. The colorimetric data are generally the most deficient and difficult to secure. An immense mass of material has been collected on the subject of vapour-pressures and densities, the greater part of which will be found in Winkelmann’s Handbook, in Landolt’s and Bornstein’s Tables, and in similar compendiums. The results vary greatly in accuracy, and are frequently vitiated by errors of temperature measurement, by chemical impurities and surface condensation, or by peculiarities of the empirical formulae employed in smoothing the observations; but it would not be within the scope of the present article to discuss these details. Even at the boiling-points the discrepancies between different observers are frequently considerable. The following table contains the most probable values for a few of these points which have been determined with the greatest care or frequency:—

(H. L. C.)

VAQUERO, a Spanish word meaning a cowherd or herdsman, and so particularly used in Mexico and Spanish America for the whole class of men employed on the large cattle-ranches or vaquerias. The word, like the corresponding Fr. vacher, cow- herd, comes from the Med. Lat. vaccarius (vacca, cow).

VAR, a department in S.E. France. It was formed in 1790 of a part of Lower Provence, but in 1860 it was reduced by the transfer of the district of Grasse to the newly formed department of the Alpes Maritimes, which is the reason why the Var does not now flow in the department to which it gives its name. It is bounded N. by the department of the Basses Alpes (the Verdon river forming the boundary), E. by that of the Alpes Maritimes (the Siagne stream forming the limit), S. by the Mediterranean, and W. by the department of the Bouches du Rh6ne. Its area is 2266 sq. m., its greatest length is about 62 m., and its greatest breadth about 56 m.

The surface of the department is very hilly, the highest point being the Signal des Chens (5620 ft.) at its north-east corner. These calcareous hills are much fissured and very dry on the highest plateaux, but are rich in springs, which is the cause of very beautiful verdure in the valleys. To the W. is the chain (3786 ft.) of the Ste Baume, wherein is the celebrated grotto (now a frequented pilgrimage place) wherein St Mary Magdalene is said to have taken refuge. This chain is connected with the hills (2329 ft.) above Toulon. The thickly wooded Montagnes des Maures (2556 ft.), which extend above the coast from Hyeres to near Frejus are separated from the Ste Baume chain by the Gapeau stream and from that of the Estérel by the Argens river: the Maures chain, with the Argens valley, forms a sort of geological island in Provence, being composed of granite, gneiss and schists. To the north of the Argens valley and in the north-eastern portion of the department rises the Estérel chain, the highest summit of which (the Mont Vinaigre) attains 2021 ft.: this chain is mainly composed of igneous rocks, with some schists and porphyry. The principal river in the department is the Argens, which traverses it from W. to E., and falls into the sea near Frejus after a course of about 68 m. Its chief tributary is the Nartuby, on which stands Draguignan, the chief town, while other streams are the Arc, the Huveaune and the Gapeau. The extreme north-western extremity of the department borders for 2 m. the Durance, which separates it from the department of Vaucluse. The coast line, which is one of the most picturesque and varied in France, runs first W. to E., from the Gulf of La Ciotat to Cape Camarat, and then S.W. to N.E., from the Gulf of St Tropez to that of La Napoule. The shore is dotted (from W. to E.) successively by the sand-covered remains of the Phocaean city of Tauroentum; the little ports of Bandol and St Nazaire ; the peninsula of Cape Sicie (on which rises the chapel of Notre Dame de la Garde, and a famous lighthouse, 1178 ft.) with its eastward projection Cape Cépet (338 ft.), bristling with fortifications, to protect the great harbour of Toulon, to the north-east; the roads of Toulon; those of Giens, on the site of the Gallo- Roman town of Pomponiana; the curious peninsula of Giens, formerly an island, but now attached to the mainland by two long spits of sand, between which lies the lagoon of Les Pesquiers, with its salines; the great anchorage of Hyeres, shut off from the Mediterranean by the hilly and wooded islands of Porquerolles, Port Cros and Le Levant; the bold promontories of the Montagnes des Maures, that divide the coast into lovely bays; Cape Camarat (1066 ft.), with a lighthouse; the deep Gulf of St Tropez, with perhaps the best natural anchorage in all Provence; the Gulf of Fréjus, where, owing to the accumulated alluvial deposits at the mouth of the Argens, the Roman port of Forum Julii is now occupied by the inland town of Frejus; the red porphyry headlands of the Esterel chain, with the roads of Agay between them; and Cape Roux (1486 ft.) looking towards Cannes, still farther N.E. The department is divided into three arrondissements (Draguignan, Brignoles and Toulon), 30 cantons and 148 communes. The climate is remarkably fine and mild on the coast, where there is complete shelter from the wind, St Raphaël (with Valescure above it) and Hyeres being now much frequented winter