4. Double image prism 15 seconds. 5. Naked eye 10 seconds. 6. Finder or binocular 20 seconds. 7. Telescope 20 seconds. 8. Observe retreat of the earth's magnetic constituents are gradually supplanting by solid truths the uncertain speculations which beset the subject which, even in untrained hands, easy and collected, undaunted and unconcerned:' still 'his.