444 



NATURE 



[April a,, 1878 



by many — and for many reasons. In the first place the 

 enormous variation in the solar activity is a fact only 

 fully realised by very few. Men grown old in the service 

 of science are as a rule as little anxious to receive new 

 ideas as men grown old in any other of the world's activi- 

 ties, and further and more than this, in the case of many 

 there is what has recently been happily termed " a 

 paralysis of the imagination " — a thing far removed from 

 scientific caution — which may and indeed certainly would 

 do much harm to scientific progress if those afflicted with 

 it had any chance of having the exclusive say in the 

 matter. 



Now that things have arrived at this stage it is well to 

 bring to the front some extracts from those papers of Sir 

 Wm. Herschel's to which reference has already been made, 

 to show the wonderful prescience of the man, and also to 

 give an idea of the valuable time which has been lost by 

 the neglect, during three-quarters of a century, to take in 

 hand the work from which he predicted such a rich harvest 

 of benefits would follow. 



His first reference to the changes going on in the sun 

 was made in 1801.^ He writes : — 



•' On a former occasion I have shown that we have great 

 reason to look upon the sun as a most magnificent habit- 

 able globe ; and, from the observations which will be 

 related in this paper, it will now be seen that all argu- 

 ments we have used before are not only confirmed, but 

 that we are encouraged to go a considerable step further 

 in the investigation of the physical and planetary con- 

 struction of the sun. The influence of this eminent body 

 on the globe we inhabit is so great and so widely diffused 

 that it becomes almost a duty for us to study the opera- 

 tions which are carried on upon the solar surface. Since 

 light and heat are so essential to our well-being, it must 

 certainly be right of us to look into the source from 

 whence they are derived, in order to see whether some 

 material advantage may not be drawn from a thorough 

 acquaintance with the causes from which they originate. 



" A similar motive engaged the Egyptians formerly to 

 study and watch the motions of the Nile and to construct 

 instruments for measuring its rise with accuracy. They 

 knew very well that it was not in their power to add one 

 single inch to the flowing waters of that wonderful river ; 

 and so, in the case of the sun's influence, we are likewise 

 fully aware that we shall never be able to occasion the 

 least alteration in the operations which are carried on in 

 the solar atmosphere. But if the Egyptians could avail 

 themselves of the indications of a good Nilometer, what 

 should hinder us from drawing as profitable consequences 

 from solar observations ? We are not only in possession 

 of photometers and thermometers, by which we can 

 measure from time to time the light and heat actually 

 received from the sun, but have more especially tele- 

 scopes, that may lead us to a discovery of the causes which 

 dispose the sun to emit more or less copiously the rays 

 which occasion either of them ; and if we should even 

 fail in this respect, we may at least succeed in becoming 

 acquainted with certain symptoms or indications, from 

 which some judgment might be formed of the temperature 

 of the seasons we are likely to have. 



" Perhaps our confidence in solar observations made 

 with this view, might not exceed that which we now place 

 on the indications of a good barometer with regard to rain 

 or fair weather ; but even then a probability of a hot 

 summer, or its contrary, would always be of greater 

 consequence than the expectation of a few fair or rainy 

 days. 



' •' Observations tending to investigate the Nature of the Sun in order to 

 find the Causes or Symptoms of its Variable Emission of Light and Heat ; 

 with Remarks on the Use that may possibly be drawn from Solar Observa- 

 tions." By William Herschel, LL.D., F.R.S., read April i6, 1801. 



"It will be easily perceived that in order to obtain such 

 an intimate knowledge of the sun as that which is required 

 for the purpose here pointed out, a true information must 

 be first procured of all the phenomena which usually 

 appear on its surface." 



He then gives those wonderful observations which 

 make this paper the basis of our knowledge of the smaller 

 units of the sun's surface, and then sums up as follows : — 



" From these two last sets of observations, one of which 

 establishes the scarcity of the luminous clouds, while the 

 other shows their great abundance, / think we may 

 reasonably concbide that there must be a manifest dif- 

 ference in the emission of light and heat from the sun. 

 It appears to me, if I may be permitted the metaphor, 

 that our sun has for some time past been labouring under 

 an indisposition, from which it is now on a fair way of 

 recovering. 



"An application of the foregoing method, however, 

 even if we were perfectly assured of its being well 

 founded, will still remain attended with considerable dif- 

 ficulties. We see how, in that simple instrument the 

 barometer, our expectations of rain and fair weather are 

 only to be had by a consideration of many circumstances 

 besides its actual elevation at the moment of inspection. 

 The tides also present us with the most complicated 

 varieties in their greatest elevation, as well as in the time 

 when they happen on the coasts of diff'erent parts of the 

 globe. The simplicity of their cause, the solar and lunar 

 attractions we might have expected, would have precluded 

 every extraordinary and seemingly discordant resulcs. 



" In a much higher degree may the influence of more or 

 less light from the sun be liable to produce a great variety 

 in the severity or mildness of the seasons of di^erent 

 climates and under different local circumstatices, yet when 

 many things which are already known to affect the tem- 

 perature of different countries and others which future 

 attention may still discover, come to be properly com- 

 bined with the results we propose to draw from solar 

 observations, we may possibly find this subject less 

 intricate than we might apprehend on a first view of it. 



"If for instance we should have a warm summer in 

 this country when phenomena observed in the sun indicate 

 the expectation of it, I should by no means consider it as 

 an unsurmountable objection, if it were shown that in 

 another country the weather had not been so favourable. 



" And if it were generally found that our prognostication 

 from solar observations held good ia any one given place 

 I should be ready to say that with proper modifications 

 they would equally succeed in every other situation. 



" Before we can generalise the influence of a certain 

 cause we ought to confine our experiment to one per- 

 manent situation, where local circumstances may be 

 supposed to act nearly alike at all times which will 

 remove a number of difficulties." 



This was in April ; in May he read another paper.^ 



" Having brought the solar observations relating to the 

 symptoms of copious emission of the light and heat of the 

 sun to the 2nd of March I gave them continued in this 

 paper to the 3rd of May. It will be seen that my expecta- 

 tions of the continuance of the symptoms which I supposed 

 favourable to such emissions, have hitherto been suffi- 

 ciently verified; and by comparing the phenomena I have 

 reported with the corresponding mildness of the season, 

 my arguments will receive a considerable support, 



" I have given the following observations without delay 

 as containing an outline of the method we ought to pursue 

 in order to establish the principles which have been pointed 

 out in my former paper. But we need not in future be at a 



' " Additional Observations tending to Investigate the Symptoms of the 

 Variable Emissions of the Light and Heat -jf the Sun ; with Trials to set 

 aside darkening Glasses by Transmitting the Solar Rays through Liquids, 

 and a few Remarks to Remove Objections that might be made against some 

 of the Arguments contained in the former Paper," by William Herschel 

 LL.D., F. R.S. Read May 14, 1801. 



