BACK NUMBERS AND VOLUMES—In reply to many interrogatories as to what back numbers and volumes of the Scientific American can be furnished, we make the following statement:—Of Volumes 1, 2 and 3—none. Of Volume 4, about 20 Nos., price 50 cts. OfVolume 5, all butfour numbers, price, In sheets, $1. OfVolume 6, all; price In sheets, $2; bound,$2,75. Of Vol. 7, all; price in sheets, $2; bonnd, $2;75. Of Vol. 8, all the back members to January 1st (No. 16, but none previous.