According to (among others) Wikipedia and Oliver Sacks (Uncle Tungsten, 2001), Thomson was an early adopter of Daltons atomic theory, presenting it much more clearly than Dalton himself.
As yet, I have not been able to find any trace of this in the «Elements». The book has been digitized by Google. The OCR, however, worked very badly in parts, whereas in others the meaning can be pretty well guessed. The pdf file can be found here (53.2 MB).
I started emendating the text, which can be, in raw form, downloaded from the same site. The partly corrected text is to be found here. I marked starting and end points of corrected passages by $$ signs. Italics were marked by <i> and </i> Feel invited to continue my effort! Any contributions can be sent to whimmelheber – here follows a peculiar sign ‐ t-online – an other, but quite common sign ‐ de.