Hey mario, this is how I found it. Go to Google, see the horizontal list starting with Web Images etc., put cursor over to more with the down arrow, expand it to a drop down menu, go down to "even more" with the arrow, expand that, go down the list to "Patent Search" and open that. Type, in the search box, the patent date and whatever will help you narrow it down faster, in this case "pendulum March 1, 1881".
You have to remember when something is marked "patented" it may mean only one aspect of the item was patented. Could be the method of construction, a certain part, a certain improvement, etc. If you have to search just by the date, you may have to go through pages before you find the right patent. Of course, a patent number is much quicker than a date.