Thanks for the advice from various members. After considering the advice and looking at numerous online reviews of mice such as
The Best Bluetooth Mouse of 2016 | Top Ten Reviews I decided the best way to solve it would be to obtain a replacement mouse that restores the convenience of the scroll function.
For the past three days I have been using a Microsoft Sculpt Touch Bluetooth mouse. Like any new device it takes a little time to get used to the feel of it. It paired with the iMac on OSX 10.9.5 straightaway. I am very pleased with it. The window has not moved. Problem solved. I should have done this a while ago.