From the abundance of clay upon its site, London is, as might be expected, a brick-built city; although the ingenuity of our age has cased miles of streets with cement, to imitate stone. This prevalence of clay is, in great measure, explanatory of the vastness of the metropolis. It is nowhere better illustrated than in the fact of "the Five Fields," (between Pimlico and Chelsea,) formerly a clayey swamp, being now the site of some of the finest mansions in London. A few years ago, the clay retained so much water that no one would build there, and "the Fields" were the terror of foot-passengers proceeding from Westminster to Chelsea after nightfall. At length, Mr. Cubitt, on examining the strata, found them to consist of clay and gravel, of inconsiderable depth. _The clay he removed, and burned into bricks; and by building upon the substratum of gravel, he converted this spot from the most unhealthy to one of the most healthy_, to the immense advantage of the ground landlord and the whole metropolis. This is one of the most perfect adaptations of the means to the end, to be found in the records of the building art. ------------------ INDIA RUBBER, A CENTURY AND A HALF SINCE. Every generation is wisest in its own conceit, and the present is continually overrated at the expense of the past. Who would have thought that India rubber cloaks were worn in South America upwards of a century since? yet such, forsooth, is the plain fact of history; and disinclined as we are to rob Mr. Macintosh of the merit of his adaptation, the invention must be awarded to another age; indeed, it is almost one of the antiquities of the New World. In a work entitled _La Monarchia Indiana_, printed at Madrid in 1723, we find a chapter devoted to "Very profitable trees in New Spain, from which there distil various liquors and resins." Among them is described a tree called _ulquahuill_, which the natives cut with a hatchet, to obtain the white, thick, and adhesive milk. This when coagulated, they made into balls, called _ulli_, which rebounded very high, when struck to the ground, and were used in various games. It was also made into shoes and sandals. The author continues:--"Our people (the Spaniards) make use of their _ulli_ to varnish their _cloaks_, made of hempen cloth, _for wet weather_, which are good to resist water, but not against the sun, by whose heat and rays the _ulli_ is dissolved." India rubber is not known in Mexico at the present day by any other name than that of _ulli_. And the oiled silk covering of hats very generally worn throughout the country by travellers is always called _ulli_. ------------------ BALLOON VOYAGE FROM LONDON TO NASSAU.