CANTON, China, Aug. 7, 1852 MESSRS. EDITORS :I have seen it stated that daguerreotypes have been taken on glass plates, and wish to ascertain whether the coating renders them opaque, so that they would not answer to be used in the place of paintings in a magic lantern. Il they could be so used it would increase the facilities for communicating truth and science to this people, especially in physiology and natural history. I wish, also, to learn the most approved and least expensive method of cleaaing rice in the United States ; the method here is quite primitive, nd leaves the process half completed. Has india rubber ever been tried as a covering for the inking rollers of the printing press, in place of composition? Will it answer? By answering these queries in your columns you will much oblige one pledged to benefit mankind to the extent of his ability. Yours, amp;c. D. VROOMAN. [The daguerreotypes on glass which we have seen, would not answer for the magie lantern. The Rice Hulling Mills, employed in South Carolinaan improved one being patented by P. MsKinlay, of Charleston, last yearare simply beetles working in a close chamber, and made to pound the rice. India rubber has been tried for printers' rollers, but it does not answer the purpose like the kind made out of molasses and glue. It is our opinion that the Scientific American finds its way into more families than any other paper (except it may be some religious ones) in the world. We have a subscriber in the capital of Siamand here is one in Canton ; and in many curious nooks and corners of the world, the contents of our columns are discussed weekly by menthe intelligent few scattered among the people of different nations, kindred, and tongues.