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 ls 2 and 3—none. Of Volume 4, about 20 Nos.; price 50 cts. Of Volume 5, all but 4 numbers, price, in sheets, $1. Of Volume 6, all; price in sheets, $2; bound, $2,75, Of Vol. 7, all; do do do