We have news from Buenos Ayres to the 18th of August. The war raging in that country is becoming more and more important, and a brief sketch of its origin and character may be useful in aiding our readers to understand the course of events. The contest is properly between Brazil and Buenos Ayres, and the prize for which the two forces are contending is the province of Uruguay. Until 1821 Uruguay was a province of Buenos Ayres; but Pedro I. of Brazil, by the lavish use of bribes and other agencies, equally potent and equally corrupt, succeeded in revolutionizing the country and attaching it to Brazil. In 1825 Uruguay declared itself free, and in 1828 it was recognized as a free government by the Plata Confederation, in which recognition Brazil was obliged to concur. Upon the abdication of Pedro, which occurred soon after, Brazil was governed by a regency of which Louis Philippe obtained complete control. France, Spain, and Portugal formed a design of re-annexing Uruguay to Brazil, and they found facile allies in this purpose in the Brazilian Court, which sought to extend the boundaries of the Empire to the coasts of the River Plata and the Uruguay, and to occupy the vast and fertile territory which they include. From that time to this, with occasional intermissions, the war has been going on. Rosas, dictator of Buenos Ayres, struggles with the strength of desperation for the recovery of Uruguay, and he is aided by Oribe, the President of Uruguay, who resists to the utmost the designs of Brazil, and prefers annexation to Buenos Ayres. Against them are the Brazilian troops, aided by Urquiza, formerly a general under Rosas, but subsequently a traitor to him and his country.

On the 20th of July Urquiza and Garzon crossed the Uruguay with a large force, which was constantly increased by desertions from the army of Oribe: they were to be joined by a Brazilian army of 12,000 men, and the war was to be carried into the heart of Buenos Ayres. On the 26th, Oribe issued a proclamation against Urquiza, and on the 30th marched with a large force to meet him. At our latest advices the troops on both sides were preparing for a grand battle, which must be, to a considerable extent, decisive of the question at issue. It is very difficult to acquire accurate and reliable information from the papers which reach us, as they are without exception partisan prints, and far more solicitous to magnify the deeds and strength of their respective parties, than to tell the truth. By the time our next Number is issued we shall probably receive decisive intelligence.

From Valparaiso our dates are to the 1st of September. Of the loan of three hundred thousand dollars asked for by the Chilian government, only seventy thousand had been raised. Two or three shocks of an earthquake had been felt at Conception, but very little injury was sustained. The coinage at the National Mint during the first half of this year, up to July 10th, had amounted to two million dollars and upward, in 127,101 gold doubloons. The Custom House receipts for the year ending 30th June, 1851, exceed those of the previous year $118,389.70. Reciprocity has been established with Austria, Belgium, Brazil, Bremen, Sardinia, Denmark, United States, France, Great Britain, Hamburg, Oldenburg, Prussia, and the Sandwich Islands. It is reported that Peru has entered into a close alliance with Brazil against Rosas. Reciprocity has been established in Chilian ports for Swedish and Norwegian vessels. The rails are laid on the Copiaco Railroad, a distance of 26 miles. On the 20th of July, the first locomotive engine ran through from Caldera to the Valley, and has since been transporting timber and iron for the extension of the track.

GREAT BRITAIN.

We have intelligence from England to the 30th of September, but there is very little worthy a place in our Record. The Queen and Court were still in Scotland, at Balmoral, and of course the public eye was turned thither for all news of interest. Parliament was not in session, but several of the members had met their constituents at county gatherings. Lord Palmerston delivered an elaborate speech at Tiverton, on the 24th, which gave material for a good deal of comment. It was a general review of the condition of the kingdom, with a vindicatory sketch of the policy pursued by the government. He dwelt eloquently on the admirable manner in which the great Exhibition had been conducted, and the excellent effect it would have upon the various nations whose representatives it had brought together. The Catholic question, the corn-laws, and the slave-trade were treated briefly and cogently. The speech was very able, and very well received. Sir Edward Bulwer Lytton, after holding himself aloof from politics for several years, has again come forward and avowed his willingness to represent the County of Hertford in Parliament. He professes a firm belief in protection principles, and expresses the belief that the present free-trade system is ruining the country. Mr. Disraeli addressed the citizens of Buckinghamshire on the 17th, the occasion being an agricultural dinner. He represented the effect of free-trade upon the leading interests of England as having been exceedingly disastrous, but avowed his conviction that the protective system could not be restored, and urged the importance of reforms in the financial administration of the country. He referred frequently to the history of his own course in Parliament, and indicated a suspicion that the new reform bill of the Ministry would prove to aim rather at curtailing the influence of the agricultural class, than to effect any desirable change. Mr. Hume met an assembly of his constituents on the 13th, at Montrose, and addressed them on the necessity of a more economical administration of public affairs, if England desired to compete with the United States. The people ought to insist, he said, upon such a new reform bill as should give every householder a vote in the national representation. This would increase the number of voters from nine hundred thousand to between three and four millions.

The vessels sent out by the English government in search of Sir John Franklin, have returned, without any further discoveries than those already recorded. The officers assert their belief that Sir John is still alive and shut up by ice, at a point beyond any which the expedition was able to reach. They have applied to the government for a steam propeller, with which, they are confident, they can reach the region where he is supposed to be confined. No answer to this application has yet been made.

The Crystal Palace continued to be crowded with visitors. The approaching close of the Exhibition had caused an increase in the number in attendance. The close is fixed for the middle of October, and notwithstanding the strenuous efforts made for its preservation, the building will probably be taken down soon after.

Hon. Abbott Lawrence, the American Minister, has been making a tour through Ireland. He was received every where with great enthusiasm. Public receptions awaited him at Galway and Limerick, and at both these cities he made brief addresses, expressing the interest taken by himself and his countrymen in the affairs of Ireland. The project of a line of steamers between Galway and the Atlantic coast was pressed upon his attention.

Emigration from Ireland continues rapidly to increase, and many towns have been almost depopulated. Every body who can get away seems inclined to leave. The census returns show that the population of Ireland has diminished very considerably within the last ten years. The potato crop promises to be generally good, though the disease has made its appearance in several localities. In all other crops the returns will be above the average.

An experiment has been made in England with a steam plow, which proved highly successful.