Stephen Johnson Field

“ The patent was for an improvement in the construction of mop-heads, which may be described, with sufficient accuracy, as an improvement in the method of moving and securing in place the movable jam or clamp of a mop-head. ”

“ With the exception of this mode of clamping, mop-heads like the plaintiff's had been in use time out of mind. Before the master, the plaintiff proved the cost of his mop-heads, and the price at which they were sold, and claimed the right to recover the difference as his damages. This rule was rejected; and, no other evidence of damages being offered, the master reported as stated. When a patent is for an improvement, and not for an entirely new machine or contrivance, the patentee must show in what particulars his improvement has added to the usefulness of the machine or contrivance. ”