I8S0.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



323 



of the atmosphere, which is equal to about three ounces. Now 

 the valve in the piston being loaded in this pro]>ortion to its supei-- 

 ficies — that is, with a weight of nine ounces— if its superficies is 

 three inches, and so on, it follows, that in the stroke of the piston 

 the valve H would not be affected till the tension of the vapour 

 became of the amount required, and, consequently, would not 

 affect the temperature of the water till it was desirable to do so; 

 and as the valve could be easily loaded with any weight, this would 

 make the apparatus self-acting. The valve I, on the top of the 

 cylinder, might be exactly balanced, so that there would be almost 

 no pressure on the piston from the tension of the vapour above it: 

 some lime also placed in a vessel on the piston would absorb the 

 moisture remaining above it. The rapidity with which water loses 

 its temperature in the exhausted receiver of an air-pump, shows 

 that a few strokes of the piston would absorb enough of the heat of 

 the water to lower it to the required temperature. 



In the removal of the vitiated air, I cannot however but think 

 that mechanical means would be far preferable to the mere open- 

 ing of a sash, as this proceeding must cause a communication with 

 the external air which would be far from desirable. And this 

 circumstance at once brings under consideration the vexed subject 

 of ventilation; that science so well understood in theory, but so 

 lamentably displayed in practice, but which is at the same time a 

 Subject of so much importance, that I cannot refrain from quoting 

 the words of a well known writer on this and similar topics. In 

 contending for the superiority of ventilation eil'ected by mecha- 

 nical means. Dr. Arnott, in his ' Treatise on Warming and Venti- 

 lating,' observes, " It is a remarkable fact that the first accomplish- 

 ment of perfect ventilation for a crowded place was not, as might 

 have been anticipated, in the houses of the great and learned, and 

 therefore in our houses of parliament or in the churches of the 

 wealthy, or in fashionable assembly rooms of any kind — but in the 

 cotton factories. In the first mentioned places it is true tliat open- 

 ings were made in the ceilings and side walls, and cowls were 

 placed over the openings or fires, or strong lamps were placed 



within them to rarify the air and cause it to ascend; but as in all 

 these cases, the important object was trusted to the working of 

 invisible draughts or currents which might not take place, and 

 which very often, from unsuspected countervailing influences, did 

 not take place aright, the object was most imperfectly accom- 

 plished. It was in the cotton-factories that fan-wheels were first 

 set in motion, which, loith a certain speed of evolution, were known 

 to extract a certain quantity of air!' — In this paragraph the merits 

 of the respective methods are fairly stated, and the plan is also 

 mentioned as simple, and certainly as effective as could be desired. 

 In conclusion, I think that our best thanks are due to the inge- 

 nious and talented author of the apparatus under consideration lor 

 his very useful invention; the resemblance of the means employed, 

 witli the circumstance wliich, as he observes, is so often stumbled 

 on by workmen, and is noticed in every work on natural philo- 

 sophy, proves to us how long a principle may be patent to o'lr 

 senses ere our minds ai'e struck by its applicability to purposes of 

 general usefulness. 



I am, &c. Q. 



THE ROUTE TO CALIFORNIA BY THE TRHUAN- 

 TEPEC ISTHMUS. 



Mr. Letcher, the American Minister at Mexico, it has been announceJ, 

 has succeeded iu effecting a treaty with the government of that country witfi 

 respect to the Tehuantepec route across the Isthmus. It is understoodt hat 

 tliis treaty is sinjilar in its character and conditions to that recently made 

 by our etBcient charge d' affairs, Mr. Squires, between our government and 

 that of Nicaragua. Tlie documents connected with the affair will soon be 

 placed before the senate of the United States. The presumption is, that 

 the stipulations do not vary widely from those incorporated in Santa Anna's 

 decree of the 1st of March, 1842; and in that of Mariano de Salas, dated 

 the 5th of November, 1846. Tlie former decree contained eleven articles, 

 and the third of the series declared that the passage across the Isthmus 

 should be neutral and common to all nations at peace with Mexico. The 

 government generally made this whole decree, upon certain terms, with Don 

 Jose de Garay, who it appears, has surrendered in some way all the conces- 

 sions orginally made to him to certain citizens of the United States residing 

 at New Orleans. 15y way of distinction, therefore, this may be termed a 

 New Orleans enterprise, though the results may be of national importance. 

 The treaty was made on the 24th of last month, and it is calculated to call 

 forth much discussion, as well as to excite great interest in every part of the 

 country. 



For many years the idea of making an easy route, either by railroad or canal 

 between the Pacific and Atlantic Oceans, has not only arrested the attention 

 of our countrymen, but the serious inquiry of several European governments. 

 A ship railroad, with a capital of 10,000,000/. sterling, was proposed at one 

 time in London, with a view of levying tolls upon all the nations of the earth. 

 This was a gigantic scheme. When the mind contemplates the possibility of 

 taking a ship into a dry dock on the Atlantic shore, of cradling it upon a car 

 with 48 wheels, running upon eight rails, of seeing it transported across tlie 

 country, and deposited in a dock upon the Pacific, the ingenuity of man 

 becomes an object of admiration. We are startled with its boldness, though 

 we can scarcely doubt the rationality of its reeources. Vast capital can 

 accomplish vast results. However, the English plan will not be carried into 

 effect in the present century. The French and the Germans have made 

 several surveys of different routes, as well as the English and Americans. That 

 by Tehuantepec may or may not be practicable. Senor Gaetano Moro's survey 

 gives a highly favourable picture of the country for the proposed road. From 

 his surveys, it seems that the entire distance from sea to sea is 135 miles in 

 a right line. It presents a wide plain from the mouth of the Coatzacoalcos 

 to the foot of the Mesa de Tarifa, which is a table-land rising to 650 feet 

 above the level of the sea, and at five miles distance decends again to the 

 plain which reaches the Pacific. Near Tehuantepec, Moro found two extensive 

 lakes, the outer separated by a narrow sandbank from the ocean, and the 

 inner and larger communicating with it l)y a channel between high banks. 

 Eight rivers flow into Ibem, and, with some improving, ships may tind har- 

 bours in these waters. From the inner lake the lapd rises very gradually to 

 the Venta de Chicapa, thence with a steeper acclivity upon Tarifa, — and 

 there is a slight declivity to a river, which is navigable for ships for the dis- 

 tance of 34 miles from its mouth on the Gulf of Mexico. Such are the rude 

 outlines of Moro's survey. 



The resources of the country are immense for timber of the best quality 

 for building a road. The facilities for cattle-feeding are complete. The 

 soil is prolific, and salt mines are abundant. The climate is agreeable and 

 mild, and usually salubrious. The advantages, therefore, for constructing a 

 road cannot be overlooked. In a commercial and political point of view, 

 however, such a road would be very desirable ; and, could it be made, would 

 add largely to the prosperity of our country. From the mouth of the Missis- 

 sippi to San Francisco, by Tehuantepec, is 1825 miles nearer than by Panama. 

 From New York 1400 miles of sea navigation would be saved, were this 

 route opened. 



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