3" 



lifting fog, but now it signifies any thin layer of vapour clouds. 

 There are really two distinct types of stratus. When cirro-stratus 

 drops and becomes denser it forms into a dense sheet, through 

 which the sun appears as a misty blue. This is called alto-stratus, 

 and is considered an intermediate type. It generally continues to 

 fall and becomes still denser. It is now regarded as a stratus, but 

 perhaps the term strato-nimbus would better describe it. From this 

 cloud steady rain often falls. The other type is met with on a line 

 day. It is a thin layer of vapour cloud, but broken up, showing 

 patches of blue sky, and at night often forming beautiful coloured 

 "corona?" round the moon. This is regarded as distinctly asso- 

 ciated with fine weather. I should suggest that the former kind be 

 designated strato-nimbus, and the latter broken stratus. Nimbus is 

 scarcely a seperate division, but is a general term for clouds from 

 which rain falls. I have now briefly described all the principal 

 kinds of clouds except two, viz., cirro-cumulus and alto-cumulus. 

 The former consists of high, small lumps, sometimes called mackerel 

 clouds. They are not infrequently arranged in parallel lines and 

 associated with cirrus. When these are lower and coarser, but 

 still finer and higher than ordinary cumulus, they are called alto- 

 cumulus. We have then the following classification, where the 

 clouds are arranged roughly in order of height : 



Cirrus, 



Cirro-stratus (alto-stratus), 



Cirro-cumulus, 



Alto-cumulus, 



Cumulus, 



Strato-cumulus, 



Cumulo-nimbus, 



Nimbus, 



Stratus. 



Having now given a brief sketch of the principal instruments 

 employed by meteorologists, and indicated a few of the rules by which 

 they endeavour to forecast the weather, I will now repeat for the 

 benefit of those who may wish to take systematic observations, some 

 of the instructions which are issued to the meterological observers 

 connected with the Perth Observatory. Private observers cannot do 

 better than conform to the same system, and I shall always be happy 

 to give any explanations or afford any assistance in my power. 



INSTRUCTIONS TO METEOROLOGICAL OBSERVERS. 



The Stevenson screen must be erected in an exposed situation, 

 with the door facing south. The bottom of the louvred box must be 

 level, and about four feet from above the ground. 



