PERFECT FIT

I have just read in your November issue Mr Addis’ letter lamenting the problem of the PVC 40 mm OD (Outside Diameter) wastepipe used as the barrel of the cannon in your August 2016 project. The problem being the pipe’s ID (Inside Diameter) being somewhat smaller than the 40 mm pingpong ball.

Rather than re-engineering a 50 mm OD PVC pipe, which would keep one entertained at length, use 40 mm HDPE (black) irrigation pipe, available at larger hardware stores and garden shops selling irrigation equipment, or even an agricultural co-op. It generally comes in two grades; class 3 for up to 3 bar pressure (which exceeds that of PVC wastepipe and, I think, is still cheaper, too); and a thicker- walled class 6 for 6 bar pressure capacity (both have the same 40 mm ID). The latter would surely test the ping-pong cannon to new extremes. DALE HILLEBRAND PINELANDS

After the discovery of a 20 000-year-old woolly mammoth carcass, breeding or cloning mammoths became a realistic scientific objective. The plan was to cross-breed the mammoth DNA with an elephant or regenerate the cells in order to clone the long extinct animal. As we don’t have any woolly mammoths walking around yet, you can guess how that went.