How to fix the error; 'Error: Bootstrap tooltips require Tether (http://github.hubspot.com/tether/)'

I'm using Bootstrap V4 and the following error is logged in the console;

Error: Bootstrap tooltips require Tether (http://github.hubspot.com/tether/)

I have tried to remove the error by installing Tether but it hasn't worked. I have 'installed' Tether by including the following lines of code;

<link rel="stylesheet" href="http://www.atlasestateagents.co.uk/css/tether.min.css">
<script src="http://www.atlasestateagents.co.uk/javascript/tether.min.js"></script>

Have I 'installed' tether correctly?

Can anyone help me remove this error?

If you wish to view the error on my site, please click here and load your console.

For Bootstrap 4 stable:

Since beta Bootstrap 4 doesn't depend on Tether but Popper.js. All scripts (must be in this order):

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>

See the current documentation for the newest script versions.

Only Bootstrap 4 alpha:

Bootstrap 4 alpha needs Tether, so you need to include tether.min.js before you include bootstrap.min.js, eg.

<script src="https://npmcdn.com/[email protected]/dist/js/tether.min.js"></script>
<script src="https://npmcdn.com/[email protected]/dist/js/bootstrap.min.js"></script>

If you're using Webpack:

1. Set up bootstrap-loader as described in docs;
2. Install tether.js via npm;
3. Add tether.js to the webpack ProvidePlugin plugin.

webpack.config.js:

plugins: [
        <... your plugins here>,
        new webpack.ProvidePlugin({
            $: "jquery",
            jQuery: "jquery",
            "window.jQuery": "jquery",
            "window.Tether": 'tether'
        })
    ]

Source