184 SECTION PHYSICS. 



ment at Kew was disturbed at the same time as the one at Lisbon. 

 Moreover, two astronomers, both now dead Mr. Carrington and Mr. 

 Hodgson were looking at the sun at the same time, and happened to 

 observe a sudden outburst of light. Mr. Chambers, who was then at 

 the Kew Observatory, observed a simultaneous disturbance of the 

 magnet. You are aware that the period of sun spots and magnetism 

 appear to be closely connected ; and it is extremely important that 

 these observations, which have been going on now with the same in- 

 strument for sixteen years, should be continued for a great number of 

 years still, and then we may have some light thrown possibly on the 

 cause of magnetism. I beg to return your thanks to Mr. Brooke, not only 

 for the account he has given us, but for what he has done for science. 



I now call on Professor Rijke, on the Historical Instruments from 

 Leyden. 



Professor RIJKE : Ladies and gentlemen, The first thing I have to 

 do is to implore your indulgence for the bad English which I am about 

 to speak, but I hope that you will remember that, if you were obliged 

 to lecture in Dutch, your Dutch would not perhaps be much better 

 than my English. I hope also that you will forgive me if I use a foreign 

 word when I cannot find the English one. I shall not lecture on the 

 services which my countrymen have rendered to science, but I intend 

 only to speak a few words on the most interesting Dutch instruments 

 of the seventeenth and eighteenth centuries which have been here ex- 

 hibited. The first instrument to wlAch I wish to draw your attention 

 is the first compound microscope which was made in Middleburg, and 

 which you see here. It consists only of two convex lenses, and was 

 made by Hans and Zacharias Janssen. There is a letter written by 

 William Boreel, Dutch ambassador in France, stating that Hans and 

 Zacharias Janssen, whom he knew perfectly well, having been their 

 neighbour at Middleburg, and having often played with them when 

 they were young, he says in that letter that compound microscopes 

 were made by the Janssens long before the year 1610. The art of 

 making compound microscopes made hardly any progress at all during 

 the 150 years which followed upon the invention of the Janssens ; and 

 indeed no progress could be made until their theory was further com- 

 pleted. It was for this reason that the great discoveries in the micro- 

 scopical^world were made by single lenses, and the man who was fore- 



